diff --git a/app/controllers/admin/users_controller.rb b/app/controllers/admin/users_controller.rb
index e83ecc11..c86b173e 100644
--- a/app/controllers/admin/users_controller.rb
+++ b/app/controllers/admin/users_controller.rb
@@ -2,13 +2,10 @@ class Admin::UsersController < Admin::BaseController
   inherit_resources
 
   def index
-    @users = User.order('nick ASC')
+    @users = User.natural_order
 
     # if somebody uses the search field:
-    unless params[:user_name].blank?
-      @users = @users.where("first_name LIKE :user_name OR last_name LIKE :user_name OR nick LIKE :user_name",
-                            user_name: "%#{params[:user_name]}%")
-    end
+    @users = @users.natural_search(params[:user_name]) unless params[:user_name].blank?
 
     @users = @users.page(params[:page]).per(@per_page)
   end
diff --git a/app/controllers/foodcoop/users_controller.rb b/app/controllers/foodcoop/users_controller.rb
index f73147bc..31539dce 100644
--- a/app/controllers/foodcoop/users_controller.rb
+++ b/app/controllers/foodcoop/users_controller.rb
@@ -1,19 +1,16 @@
 class Foodcoop::UsersController < ApplicationController
 
   def index
-    @users = User.order('nick ASC')
+    @users = User.natural_order
 
     # if somebody uses the search field:
-    unless params[:user_name].blank?
-      @users = @users.where("first_name LIKE :user_name OR last_name LIKE :user_name OR nick LIKE :user_name",
-                            user_name: "%#{params[:user_name]}%")
-    end
+    @users = @users.natural_search(params[:user_name]) unless params[:user_name].blank?
 
     if params[:ordergroup_name]
       @users = @users.joins(:groups).where("groups.type = 'Ordergroup' AND groups.name LIKE ?", "%#{params[:ordergroup_name]}%")
     end
 
-    @users = @users.page(params[:page]).per(@per_page).order('users.nick ASC')
+    @users = @users.page(params[:page]).per(@per_page)
 
     respond_to do |format|
       format.html # index.html.haml
diff --git a/app/controllers/users_controller.rb b/app/controllers/users_controller.rb
index 916b33f7..51ca228f 100644
--- a/app/controllers/users_controller.rb
+++ b/app/controllers/users_controller.rb
@@ -2,9 +2,9 @@ class UsersController < ApplicationController
 
   # Currently used to display users nick and ids for autocomplete
   def index
-    @users = User.where("nick LIKE ?", "%#{params[:q]}%")
+    @users = User.natural_search(params[:q])
     respond_to do |format|
-      format.json { render :json => @users.map { |u| u.token_attributes } }
+      format.json { render :json => @users.map(&:token_attributes) }
     end
   end
 
diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 2588ea18..59994432 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -155,13 +155,6 @@ module ApplicationHelper
       :target => "_blank"
   end
   
-  # offers a link for writing message to user
-  # checks for nil (useful for relations)
-  def link_to_user_message_if_valid(user)
-    user.nil? ? '??' : link_to(user.nick, new_message_path('message[mail_to]' => user.id),
-                               :title => I18n.t('helpers.application.write_message'))
-  end
-
   def bootstrap_flash
     flash_messages = []
     flash.each do |type, message|
@@ -183,4 +176,32 @@ module ApplicationHelper
     render :partial => 'shared/base_errors', :locals => {:error_messages => messages}
   end
 
+  # show a user, depending on settings
+  def show_user(user=@current_user, options = {})
+    if user.nil?
+      "?"
+    elsif FoodsoftConfig[:use_nick]
+      if options[:full] and options[:markup]
+        raw "<b>#{h user.nick}</b> (#{h user.first_name} #{h user.last_name})"
+      elsif options[:full]
+        "#{user.nick} (#{user.first_name} #{user.last_name})"
+      else
+        # when use_nick was changed from false to true, users may exist without nick
+        user.nick.nil? ? I18n.t('helpers.application.nick_fallback') : user.nick
+      end
+    else
+      "#{user.first_name} #{user.last_name}" + (options[:unique] ? " (\##{user.id})" : '')
+    end
+  end
+
+  # render user presentation linking to default action (write message)
+  def show_user_link(user=@current_user)
+    if user.nil?
+      show_user user
+    else
+      link_to show_user(user), new_message_path('message[mail_to]' => user.id),
+                               :title => I18n.t('helpers.application.write_message')
+    end
+  end
+
 end
diff --git a/app/helpers/tasks_helper.rb b/app/helpers/tasks_helper.rb
index c123c9ae..f2a9bea5 100644
--- a/app/helpers/tasks_helper.rb
+++ b/app/helpers/tasks_helper.rb
@@ -2,7 +2,7 @@ module TasksHelper
 
   def task_assignments(task)
     task.assignments.map do |ass|
-      content_tag :span, ass.user.nick, :class => (ass.accepted? ? 'accepted' : 'unaccepted')
+      content_tag :span, show_user(ass.user), :class => (ass.accepted? ? 'accepted' : 'unaccepted')
     end.join(", ").html_safe
   end
 
diff --git a/app/mailers/mailer.rb b/app/mailers/mailer.rb
index 30eb44a7..003e75ed 100644
--- a/app/mailers/mailer.rb
+++ b/app/mailers/mailer.rb
@@ -1,6 +1,11 @@
 # encoding: utf-8
 # ActionMailer class that handles all emails for the FoodSoft.
 class Mailer < ActionMailer::Base
+  # XXX Quick fix to allow the use of show_user. Proper take would be one of
+  #     (1) Use draper, decorate user
+  #     (2) Create a helper with this method, include here and in ApplicationHelper
+  helper :application
+  include ApplicationHelper
 
   layout 'email'  # Use views/layouts/email.txt.erb
 
@@ -15,7 +20,7 @@ class Mailer < ActionMailer::Base
 
     mail subject: "[#{FoodsoftConfig[:name]}] " + message.subject,
          to: recipient.email,
-         from: "#{message.sender.nick} <#{message.sender.email}>"
+         from: "#{show_user(message.sender)} <#{message.sender.email}>"
   end
 
   # Sends an email with instructions on how to reset the password.
@@ -26,7 +31,7 @@ class Mailer < ActionMailer::Base
     @link = new_password_url(id: @user.id, token: @user.reset_password_token)
 
     mail :to => @user.email,
-         :subject => "[#{FoodsoftConfig[:name]}] " + I18n.t('mailer.reset_password.subject', :username => @user.nick)
+         :subject => "[#{FoodsoftConfig[:name]}] " + I18n.t('mailer.reset_password.subject', :username => show_user(@user))
   end
     
   # Sends an invite email.
@@ -75,7 +80,7 @@ class Mailer < ActionMailer::Base
     @feedback = feedback
 
     mail :to => FoodsoftConfig[:notification]["error_recipients"],
-         :from => "#{user.nick} <#{user.email}>",
+         :from => "#{show_user user} <#{user.email}>",
          :sender => FoodsoftConfig[:notification]["sender_address"],
          :errors_to => FoodsoftConfig[:notification]["sender_address"],
          :subject => "[#{FoodsoftConfig[:name]}] " + I18n.t('mailer.feedback.subject', :email => user.email)
diff --git a/app/models/group.rb b/app/models/group.rb
index 092c0119..9c861abd 100644
--- a/app/models/group.rb
+++ b/app/models/group.rb
@@ -17,7 +17,7 @@ class Group < ActiveRecord::Base
   
   # Returns all NONmembers and a checks for possible multiple Ordergroup-Memberships
   def non_members
-    User.all(:order => 'nick').reject { |u| users.include?(u) }
+    User.natural_order.all.reject { |u| users.include?(u) }
   end
 
   def user_tokens=(ids)
diff --git a/app/models/message.rb b/app/models/message.rb
index e14ad59e..6504489c 100644
--- a/app/models/message.rb
+++ b/app/models/message.rb
@@ -49,7 +49,7 @@ class Message < ActiveRecord::Base
     @reply_to = Message.find(message_id)
     add_recipients([@reply_to.sender])
     self.subject = I18n.t('messages.model.reply_subject', :subject => @reply_to.subject)
-    self.body = I18n.t('messages.model.reply_header', :user => @reply_to.sender.nick, :when => I18n.l(@reply_to.created_at, :format => :short)) + "\n"
+    self.body = I18n.t('messages.model.reply_header', :user => @reply_to.sender.display, :when => I18n.l(@reply_to.created_at, :format => :short)) + "\n"
     @reply_to.body.each_line{ |l| self.body += I18n.t('messages.model.reply_indent', :line => l) }
   end
 
@@ -64,7 +64,7 @@ class Message < ActiveRecord::Base
   end
 
   def sender_name
-    system_message? ? I18n.t('layouts.foodsoft') : sender.nick rescue "??"
+    system_message? ? I18n.t('layouts.foodsoft') : sender.display rescue "?"
   end
 
   def recipients
@@ -77,7 +77,7 @@ class Message < ActiveRecord::Base
         begin
           Mailer.foodsoft_message(self, user).deliver
         rescue
-          Rails.logger.warn "Deliver failed for #{user.nick}: #{user.email}"
+          Rails.logger.warn "Deliver failed for user \##{user.id}: #{user.email}"
         end
       end
     end
diff --git a/app/models/ordergroup.rb b/app/models/ordergroup.rb
index 0188abcf..bf82afc4 100644
--- a/app/models/ordergroup.rb
+++ b/app/models/ordergroup.rb
@@ -23,7 +23,7 @@ class Ordergroup < Group
     "#{contact_phone} (#{contact_person})"
   end
   def non_members
-    User.all(:order => 'nick').reject { |u| (users.include?(u) || u.ordergroup) }
+    User.natural_order.all.reject { |u| (users.include?(u) || u.ordergroup) }
   end
 
   def value_of_open_orders(exclude = nil)
@@ -102,7 +102,7 @@ class Ordergroup < Group
   # Make sure, that a user can only be in one ordergroup
   def uniqueness_of_members
     users.each do |user|
-      errors.add :user_tokens, I18n.t('ordergroups.model.error_single_group', :user => user.nick) if user.groups.where(:type => 'Ordergroup').size > 1
+      errors.add :user_tokens, I18n.t('ordergroups.model.error_single_group', :user => user.display) if user.groups.where(:type => 'Ordergroup').size > 1
     end
   end
 
diff --git a/app/models/user.rb b/app/models/user.rb
index c46d950c..3119e29d 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -24,15 +24,19 @@ class User < ActiveRecord::Base
   # makes the current_user (logged-in-user) available in models
   cattr_accessor :current_user
   
-  validates_presence_of :nick, :email
+  validates_presence_of :email
   validates_presence_of :password, :on => :create
-  validates_length_of :nick, :in => 2..25
-  validates_uniqueness_of :nick, :case_sensitive => false
   validates_format_of :email, :with => /^([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})$/i
   validates_uniqueness_of :email, :case_sensitive => false
   validates_length_of :first_name, :in => 2..50
   validates_confirmation_of :password
   validates_length_of :password, :in => 5..25, :allow_blank => true
+  # allow nick to be nil depending on foodcoop config
+  # TODO Rails 4 may have a more beautiful way
+  #   http://stackoverflow.com/questions/19845910/conditional-allow-nil-part-of-validation
+  validates_length_of :nick, :in => 2..25, :allow_nil => true, :unless => Proc.new { FoodsoftConfig[:use_nick] }
+  validates_length_of :nick, :in => 2..25, :allow_nil => false, :if => Proc.new { FoodsoftConfig[:use_nick] }
+  validates_uniqueness_of :nick, :case_sensitive => false, :allow_nil => true # allow_nil in length validation
 
   before_validation :set_password
   after_initialize do
@@ -55,6 +59,22 @@ class User < ActiveRecord::Base
       self.settings.merge!(key, value)
     end
   end
+
+  # sorted by display name
+  def self.natural_order
+    # would be sensible to match ApplicationController#show_user
+    if FoodsoftConfig[:use_nick]
+      order('nick ASC')
+    else
+      order('first_name ASC, last_name ASC')
+    end
+  end
+
+  # search by (nick)name
+  def self.natural_search(q)
+    # we always use both nick and name, to make sure a user is found
+    where("CONCAT(first_name, CONCAT(' ', last_name)) LIKE :q OR nick LIKE :q", q: "%#{q}%")
+  end
   
   def locale
     settings.profile['language']
@@ -132,8 +152,8 @@ class User < ActiveRecord::Base
      self.groups.find(:all, :conditions => {:type => ""})
   end
 
-  def self.authenticate(nick, password)
-    user = find_by_nick(nick)
+  def self.authenticate(login, password)
+    user = (find_by_nick(login) or find_by_email(login))
     if user && user.has_password(password)
       user
     else
@@ -141,8 +161,21 @@ class User < ActiveRecord::Base
     end
   end
 
+  # XXX this is view-related; need to move out things like token_attributes
+  #     then this can be removed
+  def display
+    # would be sensible to match ApplicationHelper#show_user
+    if FoodsoftConfig[:use_nick]
+      nick.nil? ? I18n.t('helpers.application.nick_fallback') : nick
+    else
+      name
+    end
+  end
+
   def token_attributes
-    {:id => id, :name => "#{nick} (#{ordergroup.try(:name)})"}
+    # would be sensible to match ApplicationController#show_user
+    #   this should not be part of the model anyway
+    {:id => id, :name => "#{display} (#{ordergroup.try(:name)})"}
   end
 
 end
diff --git a/app/views/admin/base/index.html.haml b/app/views/admin/base/index.html.haml
index fbe63c09..ed13be09 100644
--- a/app/views/admin/base/index.html.haml
+++ b/app/views/admin/base/index.html.haml
@@ -9,13 +9,15 @@
       %table.table.table-striped
         %thead
           %tr
-            %th= t '.username'
+            - if FoodsoftConfig[:use_nick]
+              %th= t '.username'
             %th= t '.name'
             %th= t '.created_at'
         - for user in @users
           %tr{:class => cycle('even','odd', :name => 'users')}
-            %td= link_to user.nick, [:admin, user]
-            %td=h user.name
+            %td= link_to show_user(user), [:admin, user]
+            - if FoodsoftConfig[:use_nick]
+              %td= link_to user.name
             %td= format_date(user.created_on)
       = link_to t('.all_users'), admin_users_path
       |
diff --git a/app/views/admin/users/_users.html.haml b/app/views/admin/users/_users.html.haml
index 3f8b1df6..5fd16bf5 100644
--- a/app/views/admin/users/_users.html.haml
+++ b/app/views/admin/users/_users.html.haml
@@ -4,7 +4,8 @@
 %table.table.table-striped
   %thead
     %tr
-      %th= t '.login'
+      - if FoodsoftConfig[:use_nick]
+        %th= t '.login'
       %th= t '.name'
       %th= t '.email'
       %th= t 'admin.access_to'
@@ -13,8 +14,9 @@
   %tbody
     - for user in @users 
       %tr
-        %td= link_to user.nick, [:admin, user]
-        %td= user.name
+        %td= link_to show_user(user), [:admin, user]
+        - if FoodsoftConfig[:use_nick]
+          %td= user.name
         %td= user.email
         %td= format_roles(user)
         %td= format_time(user.last_login)
diff --git a/app/views/admin/users/show.html.haml b/app/views/admin/users/show.html.haml
index 4d0cd1ab..2321ccdb 100644
--- a/app/views/admin/users/show.html.haml
+++ b/app/views/admin/users/show.html.haml
@@ -1,4 +1,4 @@
-- title @user.nick
+- title show_user(@user)
 
 .row-fluid
   .span3
@@ -6,8 +6,9 @@
       %h4= t '.person'
       %p= t '.member_since', time: distance_of_time_in_words(Time.now, @user.created_on)
       %dl
-        %dt= t '.nick'
-        %dd= @user.nick
+        - if FoodsoftConfig[:use_nick]
+          %dt= t '.nick'
+          %dd= @user.nick
         %dt= t '.name'
         %dd= h @user.name
         %dt= t '.email'
diff --git a/app/views/finance/balancing/_orders.html.haml b/app/views/finance/balancing/_orders.html.haml
index 0fa52428..6973aa32 100644
--- a/app/views/finance/balancing/_orders.html.haml
+++ b/app/views/finance/balancing/_orders.html.haml
@@ -16,7 +16,7 @@
           %td= link_to truncate(order.name), new_finance_order_path(order_id: order.id)
           %td=h format_time(order.ends) unless order.ends.nil?
           %td= order.closed? ? t('.cleared', amount: number_to_currency(order.foodcoop_result)) : t('.ended')
-          %td= order.updated_by.nil? ? '??' : order.updated_by.nick
+          %td= show_user(order.updated_by)
           %td
             - unless order.closed?
               = link_to t('.clear'), new_finance_order_path(order_id: order.id), class: 'btn btn-mini btn-primary'
diff --git a/app/views/finance/financial_transactions/_transactions.html.haml b/app/views/finance/financial_transactions/_transactions.html.haml
index ecfd1c9e..64b1c938 100644
--- a/app/views/finance/financial_transactions/_transactions.html.haml
+++ b/app/views/finance/financial_transactions/_transactions.html.haml
@@ -12,6 +12,6 @@
     - @financial_transactions.each do |t|
       %tr
         %td= format_time(t.created_on)
-        %td= h t.user.nil? ? '??' : t.user.nick
+        %td= h show_user(t.user)
         %td= h t.note
         %td.currency{:style => "color:#{t.amount < 0 ? 'red' : 'black'}; width:5em"}= number_to_currency(t.amount)
diff --git a/app/views/foodcoop/ordergroups/_ordergroups.html.haml b/app/views/foodcoop/ordergroups/_ordergroups.html.haml
index 7c7780ee..20fbd0c9 100644
--- a/app/views/foodcoop/ordergroups/_ordergroups.html.haml
+++ b/app/views/foodcoop/ordergroups/_ordergroups.html.haml
@@ -13,7 +13,7 @@
     - for ordergroup in @ordergroups
       %tr
         %td= ordergroup.name
-        %td=h ordergroup.users.collect { |u| u.nick }.join(", ")
+        %td=h ordergroup.users.collect { |u| show_user(u) }.join(", ")
         %td= format_date ordergroup.orders.order('orders.starts DESC').first.try(:starts)
         %td= link_to_new_message(message_params: {group_id: ordergroup.id})
 
diff --git a/app/views/foodcoop/users/_users.html.haml b/app/views/foodcoop/users/_users.html.haml
index 1ecbb107..df39c742 100644
--- a/app/views/foodcoop/users/_users.html.haml
+++ b/app/views/foodcoop/users/_users.html.haml
@@ -4,7 +4,8 @@
 %table.table.table-striped
   %thead
     %tr
-      %th= heading_helper User, :nick
+      - if FoodsoftConfig[:use_nick]
+        %th= heading_helper User, :nick
       %th= heading_helper User, :name
       %th= heading_helper User, :email
       %th= heading_helper User, :phone
@@ -13,8 +14,9 @@
   %tbody
     - for user in @users
       %tr
-        %td= user.nick
-        %td= user.name  if @current_user.role_admin? || user.settings.profile["name_is_public"]
+        - if FoodsoftConfig[:use_nick]
+          %td= show_user user
+        %td= user.name  if @current_user.role_admin? || user.settings.profile["name_is_public"] || !FoodsoftConfig[:use_nick]
         %td= user.email if @current_user.role_admin? || user.settings.profile["email_is_public"]
         %td= user.phone if @current_user.role_admin? || user.settings.profile["phone_is_public"]
         %td= user.ordergroup_name
diff --git a/app/views/group_orders/_form.html.haml b/app/views/group_orders/_form.html.haml
index 0d299b87..a0b11791 100644
--- a/app/views/group_orders/_form.html.haml
+++ b/app/views/group_orders/_form.html.haml
@@ -30,7 +30,7 @@
         %dt= t '.note'
         %dd= @order.note
       %dt= t '.created_by'
-      %dd= link_to_user_message_if_valid(@order.created_by)
+      %dd= show_user_link(@order.created_by)
       %dt= t '.ending'
       %dd= format_time(@order.ends)
       - unless @order.stockit? or @order.supplier.min_order_quantity.blank?
@@ -40,7 +40,7 @@
       %dd= number_to_currency @order.sum
       %dt= t '.last_update'
       %dd
-        = @group_order.updated_by.nick if @group_order.updated_by
+        = show_user(@group_order.updated_by) if @group_order.updated_by
         (#{format_time(@group_order.updated_on)})
       %dt= t '.funds'
       %dd= number_to_currency(@ordering_data[:available_funds])
diff --git a/app/views/group_orders/show.html.haml b/app/views/group_orders/show.html.haml
index ed3079ca..27a88eff 100644
--- a/app/views/group_orders/show.html.haml
+++ b/app/views/group_orders/show.html.haml
@@ -22,7 +22,7 @@
       - else
         = t '.not_ordered'
     - if @order.closed?
-      %p= t '.closed_by', user: @order.updated_by.nick
+      %p= t '.closed_by', user: show_user(@order.updated_by)
       = link_to t('.comment'), "#comments"
 
 // Article box
diff --git a/app/views/home/index.html.haml b/app/views/home/index.html.haml
index 3e70be75..236d5c5c 100644
--- a/app/views/home/index.html.haml
+++ b/app/views/home/index.html.haml
@@ -57,7 +57,7 @@
         - for ft in current_user.ordergroup.financial_transactions.limit(5).order('created_on DESC')
           %tr
             %td= format_time(ft.created_on)
-            %td= h(ft.user.nil? ? '?' : ft.user.nick)
+            %td= h(show_user(ft.user))
             %td= h(ft.note)
             - color = ft.amount < 0 ? 'red' : 'black'
             %td{:style => "color:#{color}; width:5em", :class => "currency"}= number_to_currency(ft.amount)
diff --git a/app/views/home/ordergroup.html.haml b/app/views/home/ordergroup.html.haml
index 215d2826..213ef0c9 100644
--- a/app/views/home/ordergroup.html.haml
+++ b/app/views/home/ordergroup.html.haml
@@ -11,7 +11,7 @@
         = number_to_currency(@ordergroup.get_available_funds())
       %p
         %b= Ordergroup.human_attribute_name(:user_tokens) + ':'
-        = @ordergroup.memberships.map{|m| m.user.nick}.join(', ')
+        = @ordergroup.memberships.map{|m| show_user m.user}.join(', ')
       = link_to t('.invite'), new_invite_path(:id => @ordergroup), :remote => true, class: 'btn btn-primary'
   .span8
     %h2= t('.account_summary')
diff --git a/app/views/home/profile.html.haml b/app/views/home/profile.html.haml
index 6a54fce6..0b0364a1 100644
--- a/app/views/home/profile.html.haml
+++ b/app/views/home/profile.html.haml
@@ -3,7 +3,7 @@
 .row-fluid
   .span7
     %h3
-      = h(t('.user.title', user: @current_user.nick))
+      = h(t('.user.title', user: show_user))
       %small= t '.user.since', when: distance_of_time_in_words(Time.now, @current_user.created_on)
     = simple_form_for(@current_user, :url => update_profile_path) do |f|
       = render :partial => 'shared/user_form_fields', :locals => {:f => f}
diff --git a/app/views/layouts/application.html.haml b/app/views/layouts/application.html.haml
index 2feb4fa3..f926e500 100644
--- a/app/views/layouts/application.html.haml
+++ b/app/views/layouts/application.html.haml
@@ -4,7 +4,7 @@
   %ul.nav.nav-pills.pull-right
     %li.dropdown
       %a.dropdown-toggle(data-toggle="dropdown" href="#")
-        = current_user.nick
+        = show_user current_user
         %b.caret
       %ul.dropdown-menu
         %li= link_to t('.profile'), my_profile_path
diff --git a/app/views/login/accept_invitation.html.haml b/app/views/login/accept_invitation.html.haml
index 07489ebc..11865bcb 100644
--- a/app/views/login/accept_invitation.html.haml
+++ b/app/views/login/accept_invitation.html.haml
@@ -1,6 +1,6 @@
 - content_for :javascript do
   :javascript
-    $('user_nick').focus();
+    $(#{FoodsoftConfig[:use_nick] ? 'user_nick' : 'user_first_name'}).focus();
 
 - title t('.title', name: FoodsoftConfig[:name])
 = t('.body', group: h(@invite.group.name), foodcoop: h(FoodsoftConfig[:name])).html_safe
diff --git a/app/views/login/new_password.html.haml b/app/views/login/new_password.html.haml
index ea928051..2aa21e57 100644
--- a/app/views/login/new_password.html.haml
+++ b/app/views/login/new_password.html.haml
@@ -1,5 +1,5 @@
 - title t('.title')
-= t('.body', user: h(@user.nick)).html_safe
+= raw t('.body', user: h(show_user(@user)))
 = simple_form_for @user, :url => update_password_path(@user.id, :token => @user.reset_password_token) do |form|
   = form.input :password
   = form.input :password_confirmation
diff --git a/app/views/mailer/feedback.text.haml b/app/views/mailer/feedback.text.haml
index 7708e297..a63e2fdc 100644
--- a/app/views/mailer/feedback.text.haml
+++ b/app/views/mailer/feedback.text.haml
@@ -1,3 +1,3 @@
-= t '.header', user: @user.nick, date: I18n.l(Time.now, :format => :short)
+= t '.header', user: show_user(@user), date: I18n.l(Time.now, :format => :short)
 \
 = @feedback
diff --git a/app/views/mailer/negative_balance.text.haml b/app/views/mailer/negative_balance.text.haml
index 51d4f6e7..94734be5 100644
--- a/app/views/mailer/negative_balance.text.haml
+++ b/app/views/mailer/negative_balance.text.haml
@@ -1 +1 @@
-= t '.text', group: @group.name, when: @transaction.created_on.strftime('%d.%m.%Y um %H:%M'), balance: @group.account_balance, amount:@transaction.amount, note: @transaction.note, user: @transaction.user.nick, foodcoop: FoodsoftConfig[:name]
+= t '.text', group: @group.name, when: @transaction.created_on.strftime('%d.%m.%Y um %H:%M'), balance: @group.account_balance, amount:@transaction.amount, note: @transaction.note, user: show_user(@transaction.user), foodcoop: FoodsoftConfig[:name]
diff --git a/app/views/mailer/order_result.text.haml b/app/views/mailer/order_result.text.haml
index 8d64fbd2..cfe6cf78 100644
--- a/app/views/mailer/order_result.text.haml
+++ b/app/views/mailer/order_result.text.haml
@@ -1,4 +1,4 @@
-= raw t '.text0', ordergroup: @group_order.ordergroup.name, order: @order.name, when: I18n.l(@order.ends), user: @order.updated_by.nick
+= raw t '.text0', ordergroup: @group_order.ordergroup.name, order: @order.name, when: I18n.l(@order.ends), user: show_user(@order.updated_by)
 - for group_order_article in @group_order.group_order_articles.ordered.all(:include => :order_article)
   - article = group_order_article.order_article.article
   \- #{article.name}:  #{group_order_article.result} x #{article.unit} = #{group_order_article.result * article.fc_price}
diff --git a/app/views/mailer/reset_password.text.haml b/app/views/mailer/reset_password.text.haml
index fd836232..2582d317 100644
--- a/app/views/mailer/reset_password.text.haml
+++ b/app/views/mailer/reset_password.text.haml
@@ -1 +1 @@
-= raw t '.text', user: @user.nick, link: @link, expires: I18n.l(@user.reset_password_expires)
+= raw t '.text', user: show_user(@user), link: @link, expires: I18n.l(@user.reset_password_expires)
diff --git a/app/views/messages/new.haml b/app/views/messages/new.haml
index 8541b996..5d3e0c89 100644
--- a/app/views/messages/new.haml
+++ b/app/views/messages/new.haml
@@ -36,7 +36,7 @@
         = t '.list.mail', email: mail_to(FoodsoftConfig[:mailing_list_subscribe])
 
   #recipients
-    = f.input :recipient_tokens, :input_html => { 'data-pre' => User.find_all_by_id(@message.recipients_ids).map { |u| u.token_attributes }.to_json }
+    = f.input :recipient_tokens, :input_html => { 'data-pre' => User.find_all_by_id(@message.recipients_ids).map(&:token_attributes).to_json }
     = f.input :group_id, :as => :select, :collection => Group.undeleted.order('type DESC, name ASC').all.reject { |g| g.memberships.empty? }
   = f.input :private
   = f.input :subject, input_html: {class: 'input-xxlarge'}
diff --git a/app/views/orders/show.html.haml b/app/views/orders/show.html.haml
index 82d43cc2..865a83c8 100644
--- a/app/views/orders/show.html.haml
+++ b/app/views/orders/show.html.haml
@@ -13,7 +13,7 @@
       %dt= t '.note'
       %dd= @order.note
     %dt= t '.created_by'
-    %dd= link_to_user_message_if_valid(@order.created_by)
+    %dd= show_user_link(@order.created_by)
     %dt= t '.begin'
     %dd= format_time(@order.starts)
     %dt= t '.ending'
diff --git a/app/views/sessions/new.html.haml b/app/views/sessions/new.html.haml
index 09a45c39..76760654 100644
--- a/app/views/sessions/new.html.haml
+++ b/app/views/sessions/new.html.haml
@@ -12,12 +12,14 @@
 
 = form_tag sessions_path, class: 'form-horizontal' do
   .control-group
-    %label(for='nick' class='control-label')= t '.user'
+    %label(for='nick' class='control-label')
+      = User.human_attribute_name (FoodsoftConfig[:use_nick] ? :user : :email)
     .controls
       = text_field_tag 'nick', nil, autocapitalize: 'off', autocorrect: 'off'
 
   .control-group
-    %label(for='password' class='control-label')= t '.password'
+    %label(for='password' class='control-label')
+      = User.human_attribute_name :password
     .controls
       = password_field_tag 'password', nil, autocapitalize: 'off', autocorrect: 'off'
 
diff --git a/app/views/shared/_comments.haml b/app/views/shared/_comments.haml
index 27da9138..03d2c0b3 100644
--- a/app/views/shared/_comments.haml
+++ b/app/views/shared/_comments.haml
@@ -1,5 +1,5 @@
 - comments.each do |comment|
   .comment[comment]
     %strong= comment.user.try(:ordergroup_name)
-    %small (#{comment.user.try(:nick)} am #{format_time(comment.created_at)}):
+    %small (#{show_user comment.user} am #{format_time(comment.created_at)}):
     = simple_format(comment.text)
diff --git a/app/views/shared/_group.html.haml b/app/views/shared/_group.html.haml
index b9b914ce..ebd34405 100644
--- a/app/views/shared/_group.html.haml
+++ b/app/views/shared/_group.html.haml
@@ -12,7 +12,7 @@
   %dd
     - members = group.users
     = "(#{members.size})"
-    = members.collect(&:nick).join(", ")
+    = members.collect{|u| show_user(u)}.join(", ")
   - unless group.is_a?(Workgroup)
     %dt= t '.apple_limit'
     %dd= group.ignore_apple_restriction ? t('.deactivated') : t('.activated')
diff --git a/app/views/shared/_group_form_fields.html.haml b/app/views/shared/_group_form_fields.html.haml
index 44376eaf..d8401aa4 100644
--- a/app/views/shared/_group_form_fields.html.haml
+++ b/app/views/shared/_group_form_fields.html.haml
@@ -4,7 +4,7 @@
 = yield
 
 = f.input :user_tokens, :as => :string,
-  :input_html => { 'data-pre' => f.object.users.map { |u| u.token_attributes }.to_json }
+  :input_html => { 'data-pre' => f.object.users.map(&:token_attributes).to_json }
 
 - content_for :javascript do
   :javascript
diff --git a/app/views/shared/_open_orders.html.haml b/app/views/shared/_open_orders.html.haml
index 63259520..5c00c5f4 100644
--- a/app/views/shared/_open_orders.html.haml
+++ b/app/views/shared/_open_orders.html.haml
@@ -19,7 +19,7 @@
             %td= format_time(order.ends) unless order.ends.nil?
             - if group_order = order.group_order(ordergroup)
               - total += group_order.price
-              %td= "#{group_order.updated_by.nick} (#{format_time(group_order.updated_on)})"
+              %td= "#{show_user group_order.updated_by} (#{format_time(group_order.updated_on)})"
               %td.numeric= number_to_currency(group_order.price)
             - else
               %td{:colspan => 2}
diff --git a/app/views/shared/_user_form_fields.html.haml b/app/views/shared/_user_form_fields.html.haml
index bfd27f49..56701874 100644
--- a/app/views/shared/_user_form_fields.html.haml
+++ b/app/views/shared/_user_form_fields.html.haml
@@ -1,4 +1,6 @@
-= f.input :nick
+- if FoodsoftConfig[:use_nick]
+  -# use_nil option to user model validators break required mark
+  = f.input :nick, required: true
 = f.input :first_name
 = f.input :last_name
 = f.input :email
@@ -19,7 +21,8 @@
             = t 'simple_form.labels.settings.settings_group.privacy'
         = profile.input 'phone_is_public',  as: :boolean, label: false, input_html: { checked: f.object.settings.profile['phone_is_public'] }
         = profile.input 'email_is_public',  as: :boolean, label: false, input_html: { checked: f.object.settings.profile['email_is_public'] }
-        = profile.input 'name_is_public',   as: :boolean, label: false, input_html: { checked: f.object.settings.profile['name_is_public'] }
+        - if FoodsoftConfig[:use_nick]
+          = profile.input 'name_is_public',   as: :boolean, label: false, input_html: { checked: f.object.settings.profile['name_is_public'] }
   
     .settings-group
       %div{class: 'control-group'}
diff --git a/app/views/shared/_workgroup_members.haml b/app/views/shared/_workgroup_members.haml
index 960113d8..ac8fabd3 100644
--- a/app/views/shared/_workgroup_members.haml
+++ b/app/views/shared/_workgroup_members.haml
@@ -8,7 +8,8 @@
         %div{id: "collapse#{workgroup.id}", class: 'accordion-body collapse'}
           .accordion-inner
             %ul.unstyled
-              - workgroup.users.includes(:groups).order('nick').each do |user|
+              - workgroup.users.includes(:groups).natural_order.each do |user|
                 %li
-                  = user.nick
+                  = show_user(user)
                   %small (#{user.ordergroup.try(:name)})
+
diff --git a/app/views/stock_takings/new.html.haml b/app/views/stock_takings/new.html.haml
index 51239ba4..481ffdc6 100644
--- a/app/views/stock_takings/new.html.haml
+++ b/app/views/stock_takings/new.html.haml
@@ -7,7 +7,7 @@
 
 = simple_form_for(@stock_taking) do |f|
   = f.input :date, as: :date_picker
-  = f.input :note, :input_html => {:size => "28x7", :value => "#{@current_user.nick}: ..."}
+  = f.input :note, :input_html => {:size => "28x7", :value => "#{show_user @current_user, unique: true}: ..."}
   %h2= t '.stock_articles'
 
   #stock_changes
diff --git a/app/views/tasks/_form.html.haml b/app/views/tasks/_form.html.haml
index 95f3b134..78925c41 100644
--- a/app/views/tasks/_form.html.haml
+++ b/app/views/tasks/_form.html.haml
@@ -19,7 +19,7 @@
   = f.input :name
   = f.input :description, as: :text, input_html: {rows: 10}
   = f.input :duration, :as => :select, :collection => 1..3
-  = f.input :user_list, :as => :string, :input_html => { 'data-pre' => @task.users.map { |u| u.token_attributes }.to_json }
+  = f.input :user_list, :as => :string, :input_html => { 'data-pre' => @task.users.map(&:token_attributes).to_json }
   = f.input :required_users
   = f.association :workgroup
   = f.input :due_date, as: :date_picker
diff --git a/config/app_config.yml.SAMPLE b/config/app_config.yml.SAMPLE
index 594b9c70..03628c49 100644
--- a/config/app_config.yml.SAMPLE
+++ b/config/app_config.yml.SAMPLE
@@ -52,6 +52,11 @@ default: &defaults
   # not fully enforced right now, since the check is only client-side
   # minimum_balance: 0
 
+  # When use_nick is enabled, there will be a nickname field in the user form,
+  # and the option to show a nickname instead of full name to foodcoop members.
+  # Members of a user's groups and administrators can still see full names.
+  use_nick: false
+
   # email address to be used as sender
   email_sender: foodsoft@foodcoop.test
 
diff --git a/config/locales/de.yml b/config/locales/de.yml
index 669ea57a..6c776a12 100644
--- a/config/locales/de.yml
+++ b/config/locales/de.yml
@@ -1328,9 +1328,7 @@ de:
       login: Anmelden
       nojs: Achtung, Cookies und Javascript müssen aktiviert sein! %{link} bitte abschalten.
       noscript: NoScript
-      password: Passwort
       title: Foodsoft anmelden
-      user: Benutzerin
   shared:
     articles:
       ordered: Bestellt
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 3b8ff87f..63b87afc 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -797,6 +797,7 @@ en:
   helpers:
     application:
       edit_user: Edit user
+      nick_fallback: (empty username)
       role_admin: Admin
       role_article_meta: Articles
       role_finance: Finance
@@ -1332,9 +1333,7 @@ en:
       login: Login
       nojs: Attention, cookies and javascript have to be activated! Please switch off %{link}.
       noscript: NoScript
-      password: Password
       title: Foodsoft login
-      user: User
   shared:
     articles:
       ordered: Ordered
diff --git a/config/locales/fr.yml b/config/locales/fr.yml
index f8aaada7..f5e54531 100644
--- a/config/locales/fr.yml
+++ b/config/locales/fr.yml
@@ -1335,9 +1335,7 @@ fr:
       login: Te connecter
       nojs: Attention, les cookies et le javascript doivent être activés! Merci de désactiver %{link}.
       noscript: NoScript
-      password: Mot de passe
       title: Te connecter à Foodsoft
-      user: Identifiant
   shared:
     articles:
       ordered: Commandé
diff --git a/config/locales/nl.yml b/config/locales/nl.yml
index b8a55aca..02fa13d4 100644
--- a/config/locales/nl.yml
+++ b/config/locales/nl.yml
@@ -1262,9 +1262,7 @@ nl:
       login: Aanmelden
       nojs: Opgelet, cookies en javascript moeten toegelaten worden! %{link} uitzetten, alsjeblieft.
       noscript: NoScript
-      password: Wachtwoord
       title: Foodsoft aanmelden
-      user: Gebruiker
   shared:
     articles:
       ordered: Besteld
diff --git a/db/migrate/20130920201529_allow_missing_nick.rb b/db/migrate/20130920201529_allow_missing_nick.rb
new file mode 100644
index 00000000..f5b96d3e
--- /dev/null
+++ b/db/migrate/20130920201529_allow_missing_nick.rb
@@ -0,0 +1,9 @@
+class AllowMissingNick < ActiveRecord::Migration
+  def self.up
+    change_column :users, :nick, :string, :default => nil, :null => true
+  end
+
+  def self.down
+    change_column :users, :nick, :string, :default => "", :null => false
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 0d5b1326..4170d918 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20130718183101) do
+ActiveRecord::Schema.define(:version => 20130920201529) do
 
   create_table "article_categories", :force => true do |t|
     t.string "name",        :default => "", :null => false
@@ -324,7 +324,7 @@ ActiveRecord::Schema.define(:version => 20130718183101) do
   add_index "tasks", ["workgroup_id"], :name => "index_tasks_on_workgroup_id"
 
   create_table "users", :force => true do |t|
-    t.string   "nick",                   :default => "", :null => false
+    t.string   "nick"
     t.string   "password_hash",          :default => "", :null => false
     t.string   "password_salt",          :default => "", :null => false
     t.string   "first_name",             :default => "", :null => false
diff --git a/lib/foodsoft_config.rb b/lib/foodsoft_config.rb
index 71b64024..ca8952e7 100644
--- a/lib/foodsoft_config.rb
+++ b/lib/foodsoft_config.rb
@@ -9,6 +9,8 @@ class FoodsoftConfig
       set_config Rails.env
       # Overwrite scope to have a better namescope than 'production'
       self.scope = config[:default_scope] or raise "No default_scope is set"
+      # Set defaults for backward-compatibility
+      set_missing
     end
 
     # Set config and database connection for specific foodcoop
@@ -46,5 +48,13 @@ class FoodsoftConfig
       ActiveRecord::Base.establish_connection(database_config)
     end
 
+    # When new options are introduced, put backward-compatible defaults here, so that
+    # configuration files that haven't been updated, still work as they did.
+    def set_missing
+      config.replace({
+        use_nick: true
+      }.merge(config))
+    end
+
   end
-end
\ No newline at end of file
+end
diff --git a/lib/foodsoft_wiki/app/views/pages/_page_list_item.html.haml b/lib/foodsoft_wiki/app/views/pages/_page_list_item.html.haml
index 496e0720..cfd03a59 100644
--- a/lib/foodsoft_wiki/app/views/pages/_page_list_item.html.haml
+++ b/lib/foodsoft_wiki/app/views/pages/_page_list_item.html.haml
@@ -2,7 +2,7 @@
 %tr
   %td{:style => "padding-left: #{ident}px"}
     = link_to page.title, wiki_page_path(page.permalink)
-  %td #{page.user.try(:nick)} (#{format_datetime_timespec(page.updated_at, t('.date_format'))})
+  %td #{show_user page.user} (#{format_datetime_timespec(page.updated_at, t('.date_format'))})
 -if siteMap == 1
   -for child in page.children.all
     = render :partial => 'page_list_item', :locals => {:page => child, :level => level+1, :siteMap => 1}
diff --git a/lib/foodsoft_wiki/app/views/pages/show.html.haml b/lib/foodsoft_wiki/app/views/pages/show.html.haml
index 2c1d0bb1..91b7a9fc 100644
--- a/lib/foodsoft_wiki/app/views/pages/show.html.haml
+++ b/lib/foodsoft_wiki/app/views/pages/show.html.haml
@@ -17,7 +17,7 @@
       - @page.versions.reverse.each do |version|
         %li
           = link_to I18n.l(version.updated_at, :format => t('.date_format')), version_page_path(@page, :version => version.lock_version)
-          = "(#{User.find_by_id(version.updated_by).try(:nick)})"
+          = "(#{show_user(User.find_by_id(version.updated_by))})"
 
   - unless @page.children.empty?
     #subpages.well.well-small{:style => "display:none"}
@@ -48,4 +48,4 @@
     %i.icon-edit= t '.edit'
   = link_to t('.delete'), @page, class: 'btn btn-danger', :method => :delete,
     :confirm => t('.delete_confirm')
-  != '| ' + t('.last_updated', user: h(@page.user.try(:nick)), when: format_datetime(@page.updated_at))
+  != '| ' + t('.last_updated', user: show_user(@page.user), when: format_datetime(@page.updated_at))
diff --git a/lib/foodsoft_wiki/app/views/pages/version.html.haml b/lib/foodsoft_wiki/app/views/pages/version.html.haml
index 222b465d..864c4f28 100644
--- a/lib/foodsoft_wiki/app/views/pages/version.html.haml
+++ b/lib/foodsoft_wiki/app/views/pages/version.html.haml
@@ -4,7 +4,7 @@
   %h3= t '.title_version'
   %b= "#{format_datetime_timespec(@version.updated_at, t('.date_format'))}"
   %ul
-    %li= t '.author', user: User.find(@version.updated_by).nick
+    %li= t '.author', user: show_user(User.find(@version.updated_by))
     %li= link_to t('.view_current'), wiki_page_path(:permalink => @page.permalink)
     %li= link_to t('.revert'), revert_page_path(@page, :version => @version.lock_version)
 
diff --git a/spec/integration/session_spec.rb b/spec/integration/session_spec.rb
index d6942e94..aa71972d 100644
--- a/spec/integration/session_spec.rb
+++ b/spec/integration/session_spec.rb
@@ -4,7 +4,7 @@ describe 'the session', :type => :feature do
   let(:user) { create :user }
 
   describe 'login page', :type => :feature do
-    it 'is accesible' do
+    it 'is accessible' do
       get login_path
       expect(response).to be_success
     end
@@ -16,6 +16,13 @@ describe 'the session', :type => :feature do
       login user.nick, 'XX'+user.password 
       expect(page).to have_selector('.alert-error')
     end
+    it 'can log me in using an email address' do
+      visit login_path
+      fill_in 'nick', :with => user.email
+      fill_in 'password', :with => user.password
+      find('input[type=submit]').click
+      expect(page).to_not have_selector('.alert-error')
+    end
   end
 
 end
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index bc90fa01..fec01465 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -49,6 +49,16 @@ describe User do
     it 'has a unique email' do
       expect(build(:user, email: "#{user.email}")).to be_invalid
     end
+
+    it 'can authenticate using email address' do
+      expect(User.authenticate(user.email, 'blahblah')).to be_true
+    end
+
+    it 'can authenticate when there is no nick' do
+      user.nick = nil
+      expect(user).to be_valid
+      expect(User.authenticate(user.email, 'blahblah')).to be_true
+    end
   end
 
   describe 'admin' do