diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5f8bd8341..a89c9e051 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ Breaking changes:
 
 Features:
 
+- [#1403](https://github.com/rails-api/active_model_serializers/pull/1403) Add support for if/unless on attributes/associations (@beauby)
 - [#1248](https://github.com/rails-api/active_model_serializers/pull/1248) Experimental: Add support for JSON API deserialization (@beauby)
 - [#1378](https://github.com/rails-api/active_model_serializers/pull/1378) Change association blocks
   to be evaluated in *serializer* scope, rather than *association* scope. (@bf4)
diff --git a/lib/active_model/serializer/associations.rb b/lib/active_model/serializer/associations.rb
index 42e872ce4..7d87156e7 100644
--- a/lib/active_model/serializer/associations.rb
+++ b/lib/active_model/serializer/associations.rb
@@ -88,6 +88,7 @@ def associations(include_tree = DEFAULT_INCLUDE_TREE)
 
         Enumerator.new do |y|
           self.class._reflections.each do |reflection|
+            next if reflection.excluded?(self)
             key = reflection.options.fetch(:key, reflection.name)
             next unless include_tree.key?(key)
             y.yield reflection.build_association(self, instance_options)
diff --git a/lib/active_model/serializer/attribute.rb b/lib/active_model/serializer/attribute.rb
index 5c9893ca5..d3e006faa 100644
--- a/lib/active_model/serializer/attribute.rb
+++ b/lib/active_model/serializer/attribute.rb
@@ -1,13 +1,25 @@
+require 'active_model/serializer/field'
+
 module ActiveModel
   class Serializer
-    Attribute = Struct.new(:name, :block) do
-      def value(serializer)
-        if block
-          serializer.instance_eval(&block)
-        else
-          serializer.read_attribute_for_serialization(name)
-        end
-      end
+    # Holds all the meta-data about an attribute as it was specified in the
+    # ActiveModel::Serializer class.
+    #
+    # @example
+    #   class PostSerializer < ActiveModel::Serializer
+    #     attribute :content
+    #     attribute :name, key: :title
+    #     attribute :email, key: :author_email, if: :user_logged_in?
+    #     attribute :preview do
+    #       truncate(object.content)
+    #     end
+    #
+    #     def user_logged_in?
+    #       current_user.logged_in?
+    #     end
+    #   end
+    #
+    class Attribute < Field
     end
   end
 end
diff --git a/lib/active_model/serializer/attributes.rb b/lib/active_model/serializer/attributes.rb
index f57ab205d..11d39c4b2 100644
--- a/lib/active_model/serializer/attributes.rb
+++ b/lib/active_model/serializer/attributes.rb
@@ -17,6 +17,7 @@ module Attributes
         def attributes(requested_attrs = nil, reload = false)
           @attributes = nil if reload
           @attributes ||= self.class._attributes_data.each_with_object({}) do |(key, attr), hash|
+            next if attr.excluded?(self)
             next unless requested_attrs.nil? || requested_attrs.include?(key)
             hash[key] = attr.value(self)
           end
@@ -54,7 +55,7 @@ def attributes(*attrs)
         #     end
         def attribute(attr, options = {}, &block)
           key = options.fetch(:key, attr)
-          _attributes_data[key] = Attribute.new(attr, block)
+          _attributes_data[key] = Attribute.new(attr, options, block)
         end
 
         # @api private
diff --git a/lib/active_model/serializer/field.rb b/lib/active_model/serializer/field.rb
new file mode 100644
index 000000000..35e6fe263
--- /dev/null
+++ b/lib/active_model/serializer/field.rb
@@ -0,0 +1,56 @@
+module ActiveModel
+  class Serializer
+    # Holds all the meta-data about a field (i.e. attribute or association) as it was
+    # specified in the ActiveModel::Serializer class.
+    # Notice that the field block is evaluated in the context of the serializer.
+    Field = Struct.new(:name, :options, :block) do
+      # Compute the actual value of a field for a given serializer instance.
+      # @param [Serializer] The serializer instance for which the value is computed.
+      # @return [Object] value
+      #
+      # @api private
+      #
+      def value(serializer)
+        if block
+          serializer.instance_eval(&block)
+        else
+          serializer.read_attribute_for_serialization(name)
+        end
+      end
+
+      # Decide whether the field should be serialized by the given serializer instance.
+      # @param [Serializer] The serializer instance
+      # @return [Bool]
+      #
+      # @api private
+      #
+      def excluded?(serializer)
+        case condition_type
+        when :if
+          !serializer.public_send(condition)
+        when :unless
+          serializer.public_send(condition)
+        else
+          false
+        end
+      end
+
+      private
+
+      def condition_type
+        @condition_type ||=
+          if options.key?(:if)
+            :if
+          elsif options.key?(:unless)
+            :unless
+          else
+            :none
+          end
+      end
+
+      def condition
+        options[condition_type]
+      end
+    end
+  end
+end
diff --git a/lib/active_model/serializer/reflection.rb b/lib/active_model/serializer/reflection.rb
index 19eb78b80..c0287b646 100644
--- a/lib/active_model/serializer/reflection.rb
+++ b/lib/active_model/serializer/reflection.rb
@@ -1,18 +1,24 @@
+require 'active_model/serializer/field'
+
 module ActiveModel
   class Serializer
     # Holds all the meta-data about an association as it was specified in the
     # ActiveModel::Serializer class.
     #
     # @example
-    #  class PostSerializer < ActiveModel::Serializer
+    #   class PostSerializer < ActiveModel::Serializer
     #     has_one :author, serializer: AuthorSerializer
     #     has_many :comments
     #     has_many :comments, key: :last_comments do
     #       object.comments.last(1)
     #     end
-    #  end
+    #     has_many :secret_meta_data, if: :is_admin?
+    #
+    #     def is_admin?
+    #       current_user.admin?
+    #     end
+    #   end
     #
-    #  Notice that the association block is evaluated in the context of the serializer.
     #  Specifically, the association 'comments' is evaluated two different ways:
     #  1) as 'comments' and named 'comments'.
     #  2) as 'object.comments.last(1)' and named 'last_comments'.
@@ -21,20 +27,13 @@ class Serializer
     #    # [
     #    #   HasOneReflection.new(:author, serializer: AuthorSerializer),
     #    #   HasManyReflection.new(:comments)
+    #    #   HasManyReflection.new(:comments, { key: :last_comments }, #<Block>)
+    #    #   HasManyReflection.new(:secret_meta_data, { if: :is_admin? })
     #    # ]
     #
     # So you can inspect reflections in your Adapters.
     #
-    Reflection = Struct.new(:name, :options, :block) do
-      # @api private
-      def value(instance)
-        if block
-          instance.instance_eval(&block)
-        else
-          instance.read_attribute_for_serialization(name)
-        end
-      end
-
+    class Reflection < Field
       # Build association. This method is used internally to
       # build serializer's association by its reflection.
       #
diff --git a/test/serializers/associations_test.rb b/test/serializers/associations_test.rb
index 4778fb2e2..aa0cae085 100644
--- a/test/serializers/associations_test.rb
+++ b/test/serializers/associations_test.rb
@@ -238,6 +238,29 @@ def test_associations_namespaced_resources
             end
           end
         end
+
+        def test_conditional_associations
+          serializer = Class.new(ActiveModel::Serializer) do
+            belongs_to :if_assoc_included, if: :true
+            belongs_to :if_assoc_excluded, if: :false
+            belongs_to :unless_assoc_included, unless: :false
+            belongs_to :unless_assoc_excluded, unless: :true
+
+            def true
+              true
+            end
+
+            def false
+              false
+            end
+          end
+
+          model = ::Model.new
+          hash = serializable(model, serializer: serializer).serializable_hash
+          expected = { if_assoc_included: nil, unless_assoc_included: nil }
+
+          assert_equal(expected, hash)
+        end
       end
     end
   end
diff --git a/test/serializers/attribute_test.rb b/test/serializers/attribute_test.rb
index 112e7ec51..c675e0aca 100644
--- a/test/serializers/attribute_test.rb
+++ b/test/serializers/attribute_test.rb
@@ -4,7 +4,7 @@ module ActiveModel
   class Serializer
     class AttributeTest < ActiveSupport::TestCase
       def setup
-        @blog = Blog.new({ id: 1, name: 'AMS Hints', type: 'stuff' })
+        @blog = Blog.new(id: 1, name: 'AMS Hints', type: 'stuff')
         @blog_serializer = AlternateBlogSerializer.new(@blog)
       end
 
@@ -95,6 +95,29 @@ def test_virtual_attribute_block
 
         assert_equal(expected, hash)
       end
+
+      def test_conditional_attributes
+        serializer = Class.new(ActiveModel::Serializer) do
+          attribute :if_attribute_included, if: :true
+          attribute :if_attribute_excluded, if: :false
+          attribute :unless_attribute_included, unless: :false
+          attribute :unless_attribute_excluded, unless: :true
+
+          def true
+            true
+          end
+
+          def false
+            false
+          end
+        end
+
+        model = ::Model.new
+        hash = serializable(model, serializer: serializer).serializable_hash
+        expected = { if_attribute_included: nil, unless_attribute_included: nil }
+
+        assert_equal(expected, hash)
+      end
     end
   end
 end