diff --git a/lib/mv_web/live/member_live/form.ex b/lib/mv_web/live/member_live/form.ex
index 87148ad..9018563 100644
--- a/lib/mv_web/live/member_live/form.ex
+++ b/lib/mv_web/live/member_live/form.ex
@@ -21,6 +21,10 @@ defmodule MvWeb.MemberLive.Form do
   """
   use MvWeb, :live_view
 
+  alias Mv.MembershipFees
+  alias Mv.MembershipFees.MembershipFeeType
+  alias MvWeb.Helpers.MembershipFeeHelpers
+
   @impl true
   def render(assigns) do
     # Sort custom fields by name for display only
@@ -161,42 +165,46 @@ defmodule MvWeb.MemberLive.Form do
           <% end %>
         </div>
 
-        <%!-- Payment Data Section (Mockup) --%>
+        <%!-- Membership Fee Section --%>
         <div class="max-w-xl">
-          <.form_section title={gettext("Payment Data")}>
-            <div role="alert" class="alert alert-info mb-4">
-              <.icon name="hero-information-circle" class="size-5" />
-              <span>{gettext("This data is for demonstration purposes only (mockup).")}</span>
-            </div>
-
-            <div class="flex gap-8">
-              <div class="w-24">
-                <label for="mock-contribution" class="label text-sm font-medium">
-                  {gettext("Contribution")}
+          <.form_section title={gettext("Membership Fee")}>
+            <div class="space-y-4">
+              <div>
+                <label class="label">
+                  <span class="label-text font-semibold">{gettext("Membership Fee Type")}</span>
                 </label>
-                <input
-                  type="text"
-                  id="mock-contribution"
-                  value="72 €"
-                  disabled
-                  class="input input-bordered w-full bg-base-200"
-                />
-              </div>
-              <div class="w-40">
-                <label class="label text-sm font-medium">{gettext("Payment Cycle")}</label>
-                <div class="flex gap-3 mt-2">
-                  <label class="flex items-center gap-1 cursor-not-allowed opacity-60">
-                    <input type="radio" name="mock_cycle" checked disabled class="radio radio-sm" />
-                    <span class="text-sm">{gettext("monthly")}</span>
-                  </label>
-                  <label class="flex items-center gap-1 cursor-not-allowed opacity-60">
-                    <input type="radio" name="mock_cycle" disabled class="radio radio-sm" />
-                    <span class="text-sm">{gettext("yearly")}</span>
-                  </label>
-                </div>
-              </div>
-              <div class="w-24 flex items-end">
-                <.input field={@form[:paid]} label={gettext("Paid")} type="checkbox" />
+                <select
+                  class="select select-bordered w-full"
+                  name={@form[:membership_fee_type_id].name}
+                  phx-change="validate_membership_fee_type"
+                  value={@form[:membership_fee_type_id].value || ""}
+                >
+                  <option value="">{gettext("None")}</option>
+                  <%= for fee_type <- @available_fee_types do %>
+                    <option
+                      value={fee_type.id}
+                      selected={fee_type.id == @form[:membership_fee_type_id].value}
+                    >
+                      {fee_type.name} ({MembershipFeeHelpers.format_currency(fee_type.amount)}, {MembershipFeeHelpers.format_interval(
+                        fee_type.interval
+                      )})
+                    </option>
+                  <% end %>
+                </select>
+                <%= for {msg, _opts} <- @form.errors[:membership_fee_type_id] || [] do %>
+                  <p class="text-error text-sm mt-1">{msg}</p>
+                <% end %>
+                <%= if @interval_warning do %>
+                  <div class="alert alert-warning mt-2">
+                    <.icon name="hero-exclamation-triangle" class="size-5" />
+                    <span>{@interval_warning}</span>
+                  </div>
+                <% end %>
+                <p class="text-sm text-base-content/60 mt-2">
+                  {gettext(
+                    "Select a membership fee type for this member. Members can only switch between types with the same interval."
+                  )}
+                </p>
               </div>
             </div>
           </.form_section>
@@ -235,12 +243,15 @@ defmodule MvWeb.MemberLive.Form do
     member =
       case params["id"] do
         nil -> nil
-        id -> Ash.get!(Mv.Membership.Member, id)
+        id -> Ash.get!(Mv.Membership.Member, id, load: [:membership_fee_type])
       end
 
     page_title =
       if is_nil(member), do: gettext("Create Member"), else: gettext("Edit Member")
 
+    # Load available membership fee types
+    available_fee_types = load_available_fee_types(member)
+
     {:ok,
      socket
      |> assign(:return_to, return_to(params["return_to"]))
@@ -248,6 +259,8 @@ defmodule MvWeb.MemberLive.Form do
      |> assign(:initial_custom_field_values, initial_custom_field_values)
      |> assign(member: member)
      |> assign(:page_title, page_title)
+     |> assign(:available_fee_types, available_fee_types)
+     |> assign(:interval_warning, nil)
      |> assign_form()}
   end
 
@@ -256,7 +269,53 @@ defmodule MvWeb.MemberLive.Form do
 
   @impl true
   def handle_event("validate", %{"member" => member_params}, socket) do
-    {:noreply, assign(socket, form: AshPhoenix.Form.validate(socket.assigns.form, member_params))}
+    validated_form = AshPhoenix.Form.validate(socket.assigns.form, member_params)
+
+    # Check for interval mismatch if membership_fee_type_id changed
+    socket =
+      if Map.has_key?(member_params, "membership_fee_type_id") &&
+           socket.assigns.member &&
+           socket.assigns.member.membership_fee_type do
+        new_fee_type_id = member_params["membership_fee_type_id"]
+
+        if new_fee_type_id != "" &&
+             new_fee_type_id != socket.assigns.member.membership_fee_type_id do
+          new_fee_type = find_fee_type(socket.assigns.available_fee_types, new_fee_type_id)
+
+          if new_fee_type &&
+               new_fee_type.interval != socket.assigns.member.membership_fee_type.interval do
+            assign(
+              socket,
+              :interval_warning,
+              gettext(
+                "Warning: Changing from %{old_interval} to %{new_interval} is not allowed. Please select a membership fee type with the same interval.",
+                old_interval:
+                  MembershipFeeHelpers.format_interval(
+                    socket.assigns.member.membership_fee_type.interval
+                  ),
+                new_interval: MembershipFeeHelpers.format_interval(new_fee_type.interval)
+              )
+            )
+          else
+            assign(socket, :interval_warning, nil)
+          end
+        else
+          assign(socket, :interval_warning, nil)
+        end
+      else
+        socket
+      end
+
+    {:noreply, assign(socket, form: validated_form)}
+  end
+
+  def handle_event(
+        "validate_membership_fee_type",
+        %{"member" => %{"membership_fee_type_id" => fee_type_id}},
+        socket
+      ) do
+    # Same validation as above, but triggered by select change
+    handle_event("validate", %{"member" => %{"membership_fee_type_id" => fee_type_id}}, socket)
   end
 
   def handle_event("save", %{"member" => member_params}, socket) do
@@ -348,6 +407,30 @@ defmodule MvWeb.MemberLive.Form do
   defp return_path("show", nil), do: ~p"/members"
   defp return_path("show", member), do: ~p"/members/#{member.id}"
 
+  # -----------------------------------------------------------------
+  # Helper Functions
+  # -----------------------------------------------------------------
+
+  defp load_available_fee_types(member) do
+    all_types =
+      MembershipFeeType
+      |> Ash.Query.sort(name: :asc)
+      |> Ash.read!(domain: MembershipFees)
+
+    # If member has a fee type, filter to same interval
+    if member && member.membership_fee_type do
+      Enum.filter(all_types, fn type ->
+        type.interval == member.membership_fee_type.interval
+      end)
+    else
+      all_types
+    end
+  end
+
+  defp find_fee_type(fee_types, fee_type_id) do
+    Enum.find(fee_types, &(&1.id == fee_type_id))
+  end
+
   # -----------------------------------------------------------------
   # Helper Functions for Custom Fields
   # -----------------------------------------------------------------