diff --git a/reference/constraints.rst b/reference/constraints.rst
index d81a4eefd37..d068494b8a2 100644
--- a/reference/constraints.rst
+++ b/reference/constraints.rst
@@ -31,6 +31,7 @@ Validation Constraints Reference
    constraints/GreaterThanOrEqual
    constraints/Range
    constraints/DivisibleBy
+   constraints/Unique
 
    constraints/Date
    constraints/DateTime
diff --git a/reference/constraints/Collection.rst b/reference/constraints/Collection.rst
index daf59746588..12dc1e2f07a 100644
--- a/reference/constraints/Collection.rst
+++ b/reference/constraints/Collection.rst
@@ -11,6 +11,11 @@ constraint.
 This constraint can also make sure that certain collection keys are present
 and that extra keys are not present.
 
+.. seealso::
+
+    If you want to validate that all the elements of the collection are unique
+    use the :doc:`Unique constraint </reference/constraints/Unique>`.
+
 ==========  ===================================================================
 Applies to  :ref:`property or method <validation-property-target>`
 Options     - `allowExtraFields`_
diff --git a/reference/constraints/Unique.rst b/reference/constraints/Unique.rst
new file mode 100644
index 00000000000..681c4dc18b6
--- /dev/null
+++ b/reference/constraints/Unique.rst
@@ -0,0 +1,113 @@
+Unique
+======
+
+Validates that all the elements of the given collection are unique (none of them
+is present more than once). Elements are compared strictly, so ``'7'`` and ``7``
+are considered different elements (a string and an integer, respectively).
+
+.. seealso::
+
+    If you want to apply different validation constraints to the elements of a
+    collection or want to make sure that certain collection keys are present,
+    use the :doc:`Collection constraint </reference/constraints/Collection>`.
+
+.. seealso::
+
+    If you want to validate that the value of an entity property is unique among
+    all entities of the same type (e.g. the registration email of all users) use
+    the :doc:`UniqueEntity constraint </reference/constraints/UniqueEntity>`.
+
+==========  ===================================================================
+Applies to  :ref:`property or method <validation-property-target>`
+Options     - `groups`_
+            - `message`_
+            - `payload`_
+Class       :class:`Symfony\\Component\\Validator\\Constraints\\Unique`
+Validator   :class:`Symfony\\Component\\Validator\\Constraints\\UniqueValidator`
+==========  ===================================================================
+
+Basic Usage
+-----------
+
+This constraint can be applied to any property of type ``array`` or
+``\Traversable``. In the following example, ``$contactEmails`` is an array of
+strings:
+
+.. configuration-block::
+
+    .. code-block:: php-annotations
+
+        // src/Entity/Person.php
+        namespace App\Entity;
+
+        use Symfony\Component\Validator\Constraints as Assert;
+
+        class Person
+        {
+            /**
+             * @Assert\Unique
+             */
+            protected $contactEmails;
+        }
+
+    .. code-block:: yaml
+
+        # config/validator/validation.yaml
+        App\Entity\Person:
+            properties:
+                contactEmails:
+                    - Unique: ~
+
+    .. code-block:: xml
+
+        <!-- config/validator/validation.xml -->
+        <?xml version="1.0" encoding="UTF-8" ?>
+        <constraint-mapping xmlns="http://symfony.com/schema/dic/constraint-mapping"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping https://symfony.com/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">
+
+            <class name="App\Entity\Person">
+                <property name="contactEmails">
+                    <constraint name="Unique"/>
+                </property>
+            </class>
+        </constraint-mapping>
+
+    .. code-block:: php
+
+        // src/Entity/Person.php
+        namespace App\Entity;
+
+        use Symfony\Component\Validator\Mapping\ClassMetadata;
+        use Symfony\Component\Validator\Constraints as Assert;
+
+        class Person
+        {
+            public static function loadValidatorMetadata(ClassMetadata $metadata)
+            {
+                $metadata->addPropertyConstraint('contactEmails', new Assert\Unique());
+            }
+        }
+
+Options
+-------
+
+.. include:: /reference/constraints/_groups-option.rst.inc
+
+message
+~~~~~~~
+
+**type**: ``string`` **default**: ``This collection should contain only unique elements.``
+
+This is the message that will be shown if at least one element is repeated in
+the collection.
+
+You can use the following parameters in this message:
+
+=============================  ================================================
+Parameter                      Description
+=============================  ================================================
+``{{ value }}``                The repeated value
+=============================  ================================================
+
+.. include:: /reference/constraints/_payload-option.rst.inc
diff --git a/reference/constraints/UniqueEntity.rst b/reference/constraints/UniqueEntity.rst
index f6c4ddf8bce..2d2b658dee1 100644
--- a/reference/constraints/UniqueEntity.rst
+++ b/reference/constraints/UniqueEntity.rst
@@ -5,6 +5,11 @@ Validates that a particular field (or fields) in a Doctrine entity is (are)
 unique. This is commonly used, for example, to prevent a new user to register
 using an email address that already exists in the system.
 
+.. seealso::
+
+    If you want to validate that all the elements of the collection are unique
+    use the :doc:`Unique constraint </reference/constraints/Unique>`.
+
 ==========  ===================================================================
 Applies to  :ref:`class <validation-class-target>`
 Options     - `em`_
diff --git a/reference/constraints/map.rst.inc b/reference/constraints/map.rst.inc
index 4f95a168242..1ccfc1ec691 100644
--- a/reference/constraints/map.rst.inc
+++ b/reference/constraints/map.rst.inc
@@ -37,6 +37,7 @@ Comparison Constraints
 * :doc:`GreaterThanOrEqual </reference/constraints/GreaterThanOrEqual>`
 * :doc:`Range </reference/constraints/Range>`
 * :doc:`DivisibleBy </reference/constraints/DivisibleBy>`
+* :doc:`Unique </reference/constraints/Unique>`
 
 Date Constraints
 ~~~~~~~~~~~~~~~~