diff --git a/lib/membership/custom_field.ex b/lib/membership/custom_field.ex
index f155968..90bbcaa 100644
--- a/lib/membership/custom_field.ex
+++ b/lib/membership/custom_field.ex
@@ -15,17 +15,18 @@ defmodule Mv.Membership.CustomField do
   - `required` - If true, all members must have this custom field (future feature)
 
   ## Supported Value Types
-  - `:string` - Text data (unlimited length)
+  - `:string` - Text data (max 10,000 characters)
   - `:integer` - Numeric data (64-bit integers)
   - `:boolean` - True/false flags
   - `:date` - Date values (no time component)
-  - `:email` - Validated email addresses
+  - `:email` - Validated email addresses (max 254 characters)
 
   ## Relationships
   - `has_many :custom_field_values` - All custom field values of this type
 
   ## Constraints
   - Name must be unique across all custom fields
+  - Name maximum length: 100 characters
   - Cannot delete a custom field that has existing custom field values (RESTRICT)
 
   ## Examples
@@ -60,14 +61,26 @@ defmodule Mv.Membership.CustomField do
   attributes do
     uuid_primary_key :id
 
-    attribute :name, :string, allow_nil?: false, public?: true
+    attribute :name, :string,
+      allow_nil?: false,
+      public?: true,
+      constraints: [
+        max_length: 100,
+        trim?: true
+      ]
 
     attribute :value_type, :atom,
       constraints: [one_of: [:string, :integer, :boolean, :date, :email]],
       allow_nil?: false,
       description: "Defines the datatype `CustomFieldValue.value` is interpreted as"
 
-    attribute :description, :string, allow_nil?: true, public?: true
+    attribute :description, :string,
+      allow_nil?: true,
+      public?: true,
+      constraints: [
+        max_length: 500,
+        trim?: true
+      ]
 
     attribute :immutable, :boolean,
       default: false,
diff --git a/lib/membership/custom_field_value.ex b/lib/membership/custom_field_value.ex
index 6e6c95f..2d6c025 100644
--- a/lib/membership/custom_field_value.ex
+++ b/lib/membership/custom_field_value.ex
@@ -30,6 +30,11 @@ defmodule Mv.Membership.CustomFieldValue do
   ## Constraints
   - Each member can have only one custom field value per custom field (unique composite index)
   - Custom field values are deleted when the associated member is deleted (CASCADE)
+  - String values maximum length: 10,000 characters
+  - Email values maximum length: 254 characters (RFC 5321)
+
+  ## Future Features
+  - Type-matching validation (value type must match custom field's value_type) - to be implemented
   """
   use Ash.Resource,
     domain: Mv.Membership,
@@ -56,11 +61,25 @@ defmodule Mv.Membership.CustomFieldValue do
       constraints: [
         storage: :type_and_value,
         types: [
-          boolean: [type: :boolean],
-          date: [type: :date],
-          integer: [type: :integer],
-          string: [type: :string],
-          email: [type: Mv.Membership.Email]
+          boolean: [
+            type: :boolean
+          ],
+          date: [
+            type: :date
+          ],
+          integer: [
+            type: :integer
+          ],
+          string: [
+            type: :string,
+            constraints: [
+              max_length: 10_000,
+              trim?: true
+            ]
+          ],
+          email: [
+            type: Mv.Membership.Email
+          ]
         ]
       ]
   end
diff --git a/test/membership/custom_field_validation_test.exs b/test/membership/custom_field_validation_test.exs
new file mode 100644
index 0000000..d8a5bd9
--- /dev/null
+++ b/test/membership/custom_field_validation_test.exs
@@ -0,0 +1,206 @@
+defmodule Mv.Membership.CustomFieldValidationTest do
+  @moduledoc """
+  Tests for CustomField validation constraints.
+  
+  Tests cover:
+  - Name length validation (max 100 characters)
+  - Name trimming
+  - Description length validation (max 500 characters)
+  - Description trimming
+  - Required vs optional fields
+  """
+  use Mv.DataCase, async: true
+
+  alias Mv.Membership.CustomField
+
+  describe "name validation" do
+    test "accepts name with exactly 100 characters" do
+      name = String.duplicate("a", 100)
+
+      assert {:ok, custom_field} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: name,
+                 value_type: :string
+               })
+               |> Ash.create()
+
+      assert custom_field.name == name
+      assert String.length(custom_field.name) == 100
+    end
+
+    test "rejects name with 101 characters" do
+      name = String.duplicate("a", 101)
+
+      assert {:error, changeset} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: name,
+                 value_type: :string
+               })
+               |> Ash.create()
+
+      assert [%{field: :name, message: message}] = changeset.errors
+      assert message =~ "max" or message =~ "length" or message =~ "100"
+    end
+
+    test "trims whitespace from name" do
+      assert {:ok, custom_field} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "  test_field  ",
+                 value_type: :string
+               })
+               |> Ash.create()
+
+      assert custom_field.name == "test_field"
+    end
+
+    test "rejects empty name" do
+      assert {:error, changeset} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "",
+                 value_type: :string
+               })
+               |> Ash.create()
+
+      assert Enum.any?(changeset.errors, fn error -> error.field == :name end)
+    end
+
+    test "rejects nil name" do
+      assert {:error, changeset} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 value_type: :string
+               })
+               |> Ash.create()
+
+      assert Enum.any?(changeset.errors, fn error -> error.field == :name end)
+    end
+  end
+
+  describe "description validation" do
+    test "accepts description with exactly 500 characters" do
+      description = String.duplicate("a", 500)
+
+      assert {:ok, custom_field} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "test_field",
+                 value_type: :string,
+                 description: description
+               })
+               |> Ash.create()
+
+      assert custom_field.description == description
+      assert String.length(custom_field.description) == 500
+    end
+
+    test "rejects description with 501 characters" do
+      description = String.duplicate("a", 501)
+
+      assert {:error, changeset} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "test_field",
+                 value_type: :string,
+                 description: description
+               })
+               |> Ash.create()
+
+      assert [%{field: :description, message: message}] = changeset.errors
+      assert message =~ "max" or message =~ "length" or message =~ "500"
+    end
+
+    test "trims whitespace from description" do
+      assert {:ok, custom_field} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "test_field",
+                 value_type: :string,
+                 description: "  A nice description  "
+               })
+               |> Ash.create()
+
+      assert custom_field.description == "A nice description"
+    end
+
+    test "accepts nil description (optional field)" do
+      assert {:ok, custom_field} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "test_field",
+                 value_type: :string
+               })
+               |> Ash.create()
+
+      assert custom_field.description == nil
+    end
+
+    test "accepts empty description after trimming" do
+      assert {:ok, custom_field} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "test_field",
+                 value_type: :string,
+                 description: "   "
+               })
+               |> Ash.create()
+
+      # After trimming whitespace, becomes nil (empty strings are converted to nil)
+      assert custom_field.description == nil
+    end
+  end
+
+  describe "name uniqueness" do
+    test "rejects duplicate names" do
+      assert {:ok, _} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "unique_field",
+                 value_type: :string
+               })
+               |> Ash.create()
+
+      assert {:error, changeset} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "unique_field",
+                 value_type: :integer
+               })
+               |> Ash.create()
+
+      assert Enum.any?(changeset.errors, fn error -> error.field == :name end)
+    end
+  end
+
+  describe "value_type validation" do
+    test "accepts all valid value types" do
+      for value_type <- [:string, :integer, :boolean, :date, :email] do
+        assert {:ok, custom_field} =
+                 CustomField
+                 |> Ash.Changeset.for_create(:create, %{
+                   name: "field_#{value_type}",
+                   value_type: value_type
+                 })
+                 |> Ash.create()
+
+        assert custom_field.value_type == value_type
+      end
+    end
+
+    test "rejects invalid value type" do
+      assert {:error, changeset} =
+               CustomField
+               |> Ash.Changeset.for_create(:create, %{
+                 name: "invalid_field",
+                 value_type: :invalid_type
+               })
+               |> Ash.create()
+
+      assert [%{field: :value_type}] = changeset.errors
+    end
+  end
+end
+
diff --git a/test/membership/custom_field_value_validation_test.exs b/test/membership/custom_field_value_validation_test.exs
new file mode 100644
index 0000000..ce5b5c6
--- /dev/null
+++ b/test/membership/custom_field_value_validation_test.exs
@@ -0,0 +1,276 @@
+defmodule Mv.Membership.CustomFieldValueValidationTest do
+  @moduledoc """
+  Tests for CustomFieldValue validation constraints.
+  
+  Tests cover:
+  - String value length validation (max 10,000 characters)
+  - String value trimming
+  - Email value validation (via Email type)
+  - Optional values (nil allowed)
+  """
+  use Mv.DataCase, async: true
+
+  alias Mv.Membership.{CustomField, CustomFieldValue, Member}
+
+  setup do
+    # Create a test member
+    {:ok, member} =
+      Member
+      |> Ash.Changeset.for_create(:create_member, %{
+        first_name: "Test",
+        last_name: "User",
+        email: "test.validation@example.com"
+      })
+      |> Ash.create()
+
+    # Create custom fields for different types
+    {:ok, string_field} =
+      CustomField
+      |> Ash.Changeset.for_create(:create, %{
+        name: "string_field",
+        value_type: :string
+      })
+      |> Ash.create()
+
+    {:ok, integer_field} =
+      CustomField
+      |> Ash.Changeset.for_create(:create, %{
+        name: "integer_field",
+        value_type: :integer
+      })
+      |> Ash.create()
+
+    {:ok, email_field} =
+      CustomField
+      |> Ash.Changeset.for_create(:create, %{
+        name: "email_field",
+        value_type: :email
+      })
+      |> Ash.create()
+
+    %{
+      member: member,
+      string_field: string_field,
+      integer_field: integer_field,
+      email_field: email_field
+    }
+  end
+
+  describe "string value length validation" do
+    test "accepts string value with exactly 10,000 characters", %{
+      member: member,
+      string_field: string_field
+    } do
+      value_string = String.duplicate("a", 10_000)
+
+      assert {:ok, custom_field_value} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: string_field.id,
+                 value: %{
+                   "_union_type" => "string",
+                   "_union_value" => value_string
+                 }
+               })
+               |> Ash.create()
+
+      assert custom_field_value.value.value == value_string
+      assert String.length(custom_field_value.value.value) == 10_000
+    end
+
+    test "rejects string value with 10,001 characters", %{
+      member: member,
+      string_field: string_field
+    } do
+      value_string = String.duplicate("a", 10_001)
+
+      assert {:error, changeset} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: string_field.id,
+                 value: %{"_union_type" => "string", "_union_value" => value_string}
+               })
+               |> Ash.create()
+
+      assert Enum.any?(changeset.errors, fn error ->
+               error.field == :value and (error.message =~ "max" or error.message =~ "length")
+             end)
+    end
+
+    test "trims whitespace from string value", %{member: member, string_field: string_field} do
+      assert {:ok, custom_field_value} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: string_field.id,
+                 value: %{"_union_type" => "string", "_union_value" => "  test value  "}
+               })
+               |> Ash.create()
+
+      assert custom_field_value.value.value == "test value"
+    end
+
+    test "accepts empty string value", %{member: member, string_field: string_field} do
+      assert {:ok, custom_field_value} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: string_field.id,
+                 value: %{"_union_type" => "string", "_union_value" => ""}
+               })
+               |> Ash.create()
+
+      # Empty strings after trimming become nil
+      assert custom_field_value.value.value == nil
+    end
+
+    test "accepts string with special characters", %{member: member, string_field: string_field} do
+      special_string = "Hello 世界! 🎉 @#$%^&*()"
+
+      assert {:ok, custom_field_value} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: string_field.id,
+                 value: %{"_union_type" => "string", "_union_value" => special_string}
+               })
+               |> Ash.create()
+
+      assert custom_field_value.value.value == special_string
+    end
+  end
+
+  describe "integer value validation" do
+    test "accepts valid integer value", %{member: member, integer_field: integer_field} do
+      assert {:ok, custom_field_value} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: integer_field.id,
+                 value: %{"_union_type" => "integer", "_union_value" => 42}
+               })
+               |> Ash.create()
+
+      assert custom_field_value.value.value == 42
+    end
+
+    test "accepts negative integer", %{member: member, integer_field: integer_field} do
+      assert {:ok, custom_field_value} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: integer_field.id,
+                 value: %{"_union_type" => "integer", "_union_value" => -100}
+               })
+               |> Ash.create()
+
+      assert custom_field_value.value.value == -100
+    end
+
+    test "accepts zero", %{member: member, integer_field: integer_field} do
+      assert {:ok, custom_field_value} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: integer_field.id,
+                 value: %{"_union_type" => "integer", "_union_value" => 0}
+               })
+               |> Ash.create()
+
+      assert custom_field_value.value.value == 0
+    end
+  end
+
+  describe "email value validation" do
+    test "accepts valid email", %{member: member, email_field: email_field} do
+      assert {:ok, custom_field_value} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: email_field.id,
+                 value: %{"_union_type" => "email", "_union_value" => "test@example.com"}
+               })
+               |> Ash.create()
+
+      assert custom_field_value.value.value == "test@example.com"
+    end
+
+    test "rejects invalid email format", %{member: member, email_field: email_field} do
+      assert {:error, changeset} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: email_field.id,
+                 value: %{"_union_type" => "email", "_union_value" => "not-an-email"}
+               })
+               |> Ash.create()
+
+      assert Enum.any?(changeset.errors, fn error -> error.field == :value end)
+    end
+
+    test "rejects email longer than 254 characters", %{member: member, email_field: email_field} do
+      # Create an email with >254 chars (243 + 12 = 255)
+      long_email = String.duplicate("a", 243) <> "@example.com"
+
+      assert {:error, changeset} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: email_field.id,
+                 value: %{"_union_type" => "email", "_union_value" => long_email}
+               })
+               |> Ash.create()
+
+      assert Enum.any?(changeset.errors, fn error -> error.field == :value end)
+    end
+
+    test "trims whitespace from email", %{member: member, email_field: email_field} do
+      assert {:ok, custom_field_value} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: email_field.id,
+                 value: %{"_union_type" => "email", "_union_value" => "  test@example.com  "}
+               })
+               |> Ash.create()
+
+      assert custom_field_value.value.value == "test@example.com"
+    end
+  end
+
+  describe "uniqueness constraint" do
+    test "rejects duplicate custom_field_id per member", %{
+      member: member,
+      string_field: string_field
+    } do
+      # Create first custom field value
+      assert {:ok, _} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: string_field.id,
+                 value: %{"_union_type" => "string", "_union_value" => "first value"}
+               })
+               |> Ash.create()
+
+      # Try to create second custom field value with same custom_field_id for same member
+      assert {:error, changeset} =
+               CustomFieldValue
+               |> Ash.Changeset.for_create(:create, %{
+                 member_id: member.id,
+                 custom_field_id: string_field.id,
+                 value: %{"_union_type" => "string", "_union_value" => "second value"}
+               })
+               |> Ash.create()
+
+      # Should have uniqueness error
+      assert Enum.any?(changeset.errors, fn error ->
+               error.message =~ "unique" or error.message =~ "already exists" or
+                 error.message =~ "has already been taken"
+             end)
+    end
+  end
+end
+