diff --git a/backend/api/managers.py b/backend/api/managers.py
index cdf04f03..4294e515 100644
--- a/backend/api/managers.py
+++ b/backend/api/managers.py
@@ -29,6 +29,26 @@ class AnnotationManager(Manager):
             distribution[username][label] = count
         return distribution
 
+    def can_annotate(self, label, project) -> bool:
+        raise NotImplementedError('Please implement this method in the subclass')
+
+
+class CategoryManager(AnnotationManager):
+
+    def get_labels(self, label, project):
+        if project.collaborative_annotation:
+            return self.filter(example=label.example)
+        else:
+            return self.filter(example=label.example, user=label.user)
+
+    def can_annotate(self, label, project) -> bool:
+        is_exclusive = project.single_class_classification
+        categories = self.get_labels(label, project)
+        if is_exclusive:
+            return not categories.exists()
+        else:
+            return not categories.filter(label=label.label).exists()
+
 
 class ExampleManager(Manager):
 
diff --git a/backend/api/models.py b/backend/api/models.py
index f12f281e..d2a3f18a 100644
--- a/backend/api/models.py
+++ b/backend/api/models.py
@@ -8,7 +8,8 @@ from django.core.exceptions import ValidationError
 from django.db import models
 from polymorphic.models import PolymorphicModel
 
-from .managers import AnnotationManager, ExampleManager, ExampleStateManager
+from .managers import (AnnotationManager, CategoryManager, ExampleManager,
+                       ExampleStateManager)
 
 DOCUMENT_CLASSIFICATION = 'DocumentClassification'
 SEQUENCE_LABELING = 'SequenceLabeling'
@@ -334,6 +335,7 @@ class Annotation(models.Model):
 
 
 class Category(Annotation):
+    objects = CategoryManager()
     example = models.ForeignKey(
         to=Example,
         on_delete=models.CASCADE,
diff --git a/backend/api/tests/test_category.py b/backend/api/tests/test_category.py
new file mode 100644
index 00000000..9d007a80
--- /dev/null
+++ b/backend/api/tests/test_category.py
@@ -0,0 +1,133 @@
+import abc
+
+from django.test import TestCase
+from model_mommy import mommy
+
+from api.models import DOCUMENT_CLASSIFICATION, Category
+
+from .api.utils import prepare_project
+
+
+class TestCategoryAnnotation(abc.ABC, TestCase):
+    exclusive = True
+    collaborative = False
+
+    @classmethod
+    def setUpTestData(cls):
+        cls.project = prepare_project(
+            DOCUMENT_CLASSIFICATION,
+            single_class_classification=cls.exclusive,
+            collaborative_annotation=cls.collaborative
+        )
+        cls.example = mommy.make('Example', project=cls.project.item)
+        cls.label_type = mommy.make('CategoryType', project=cls.project.item)
+        users = cls.project.users
+        cls.user = users[0]
+        cls.another_user = users[1]
+        cls.category = Category(
+            example=cls.example,
+            label=cls.label_type,
+            user=cls.user
+        )
+
+    def test_can_annotate_category_to_unannotated_data(self):
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertTrue(can_annotate)
+
+
+class TestExclusiveCategoryAnnotation(TestCategoryAnnotation):
+    exclusive = True
+    collaborative = False
+
+    def test_cannot_annotate_different_category_to_annotated_data(self):
+        mommy.make('Category', example=self.example, user=self.user)
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertFalse(can_annotate)
+
+    def test_cannot_annotate_same_category_to_annotated_data(self):
+        mommy.make('Category', example=self.example, label=self.label_type, user=self.user)
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertFalse(can_annotate)
+
+    def test_allow_another_user_to_annotate_same_category(self):
+        mommy.make(
+            'Category',
+            example=self.example,
+            label=self.label_type,
+            user=self.another_user
+        )
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertTrue(can_annotate)
+
+
+class TestNonExclusiveCategoryAnnotation(TestCategoryAnnotation):
+    exclusive = False
+    collaborative = False
+
+    def test_can_annotate_different_category_to_annotated_data(self):
+        mommy.make('Category', example=self.example, user=self.user)
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertTrue(can_annotate)
+
+    def test_cannot_annotate_same_category_to_annotated_data(self):
+        mommy.make('Category', example=self.example, label=self.label_type, user=self.user)
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertFalse(can_annotate)
+
+    def test_allow_another_user_to_annotate_same_category(self):
+        mommy.make(
+            'Category',
+            example=self.example,
+            label=self.label_type,
+            user=self.another_user
+        )
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertTrue(can_annotate)
+
+
+class TestCollaborativeExclusiveCategoryAnnotation(TestCategoryAnnotation):
+    exclusive = True
+    collaborative = True
+
+    def test_deny_another_user_to_annotate_same_category(self):
+        mommy.make(
+            'Category',
+            example=self.example,
+            label=self.label_type,
+            user=self.another_user
+        )
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertFalse(can_annotate)
+
+    def test_deny_another_user_to_annotate_different_category(self):
+        mommy.make(
+            'Category',
+            example=self.example,
+            user=self.another_user
+        )
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertFalse(can_annotate)
+
+
+class TestCollaborativeNonExclusiveCategoryAnnotation(TestCategoryAnnotation):
+    exclusive = False
+    collaborative = True
+
+    def test_deny_another_user_to_annotate_same_category(self):
+        mommy.make(
+            'Category',
+            example=self.example,
+            label=self.label_type,
+            user=self.another_user
+        )
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertFalse(can_annotate)
+
+    def test_allow_another_user_to_annotate_different_category(self):
+        mommy.make(
+            'Category',
+            example=self.example,
+            user=self.another_user
+        )
+        can_annotate = Category.objects.can_annotate(self.category, self.project.item)
+        self.assertTrue(can_annotate)