diff --git a/moto/codepipeline/exceptions.py b/moto/codepipeline/exceptions.py
index e455298cd..a4db9aab1 100644
--- a/moto/codepipeline/exceptions.py
+++ b/moto/codepipeline/exceptions.py
@@ -26,3 +26,19 @@ class ResourceNotFoundException(JsonRESTError):
         super(ResourceNotFoundException, self).__init__(
             "ResourceNotFoundException", message
         )
+
+
+class InvalidTagsException(JsonRESTError):
+    code = 400
+
+    def __init__(self, message):
+        super(InvalidTagsException, self).__init__("InvalidTagsException", message)
+
+
+class TooManyTagsException(JsonRESTError):
+    code = 400
+
+    def __init__(self, arn):
+        super(TooManyTagsException, self).__init__(
+            "TooManyTagsException", "Tag limit exceeded for resource [{}].".format(arn)
+        )
diff --git a/moto/codepipeline/models.py b/moto/codepipeline/models.py
index 888491296..4a8b89617 100644
--- a/moto/codepipeline/models.py
+++ b/moto/codepipeline/models.py
@@ -12,6 +12,8 @@ from moto.codepipeline.exceptions import (
     InvalidStructureException,
     PipelineNotFoundException,
     ResourceNotFoundException,
+    InvalidTagsException,
+    TooManyTagsException,
 )
 from moto.core import BaseBackend, BaseModel
 
@@ -54,6 +56,18 @@ class CodePipeline(BaseModel):
 
         return pipeline
 
+    def validate_tags(self, tags):
+        for tag in tags:
+            if tag["key"].startswith("aws:"):
+                raise InvalidTagsException(
+                    "Not allowed to modify system tags. "
+                    "System tags start with 'aws:'. "
+                    "msg=[Caller is an end user and not allowed to mutate system tags]"
+                )
+
+        if (len(self.tags) + len(tags)) > 50:
+            raise TooManyTagsException(self._arn)
+
 
 class CodePipelineBackend(BaseBackend):
     def __init__(self):
@@ -93,6 +107,8 @@ class CodePipelineBackend(BaseBackend):
         self.pipelines[pipeline["name"]] = CodePipeline(region, pipeline)
 
         if tags:
+            self.pipelines[pipeline["name"]].validate_tags(tags)
+
             new_tags = {tag["key"]: tag["value"] for tag in tags}
             self.pipelines[pipeline["name"]].tags.update(new_tags)
 
@@ -160,6 +176,22 @@ class CodePipelineBackend(BaseBackend):
 
         return tags
 
+    def tag_resource(self, arn, tags):
+        name = arn.split(":")[-1]
+        pipeline = self.pipelines.get(name)
+
+        if not pipeline:
+            raise ResourceNotFoundException(
+                "The account with id '{0}' does not include a pipeline with the name '{1}'".format(
+                    ACCOUNT_ID, name
+                )
+            )
+
+        pipeline.validate_tags(tags)
+
+        for tag in tags:
+            pipeline.tags.update({tag["key"]: tag["value"]})
+
 
 codepipeline_backends = {}
 for region in Session().get_available_regions("codepipeline"):
diff --git a/moto/codepipeline/responses.py b/moto/codepipeline/responses.py
index 75a2ce800..df1bf220f 100644
--- a/moto/codepipeline/responses.py
+++ b/moto/codepipeline/responses.py
@@ -46,3 +46,10 @@ class CodePipelineResponse(BaseResponse):
         )
 
         return json.dumps({"tags": tags})
+
+    def tag_resource(self):
+        self.codepipeline_backend.tag_resource(
+            self._get_param("resourceArn"), self._get_param("tags")
+        )
+
+        return ""
diff --git a/tests/test_codepipeline/test_codepipeline.py b/tests/test_codepipeline/test_codepipeline.py
index b93a15fc7..e71e24f76 100644
--- a/tests/test_codepipeline/test_codepipeline.py
+++ b/tests/test_codepipeline/test_codepipeline.py
@@ -530,6 +530,78 @@ def test_list_tags_for_resource_errors():
     )
 
 
+@mock_codepipeline
+def test_tag_resource():
+    client = boto3.client("codepipeline", region_name="us-east-1")
+    name = "test-pipeline"
+    create_basic_codepipeline(client, name)
+
+    client.tag_resource(
+        resourceArn="arn:aws:codepipeline:us-east-1:123456789012:{}".format(name),
+        tags=[{"key": "key-2", "value": "value-2"}],
+    )
+
+    response = client.list_tags_for_resource(
+        resourceArn="arn:aws:codepipeline:us-east-1:123456789012:{}".format(name)
+    )
+    response["tags"].should.equal(
+        [{"key": "key", "value": "value"}, {"key": "key-2", "value": "value-2"}]
+    )
+
+
+@mock_codepipeline
+def test_tag_resource_errors():
+    client = boto3.client("codepipeline", region_name="us-east-1")
+    name = "test-pipeline"
+    create_basic_codepipeline(client, name)
+
+    with assert_raises(ClientError) as e:
+        client.tag_resource(
+            resourceArn="arn:aws:codepipeline:us-east-1:123456789012:not-existing",
+            tags=[{"key": "key-2", "value": "value-2"}],
+        )
+    ex = e.exception
+    ex.operation_name.should.equal("TagResource")
+    ex.response["ResponseMetadata"]["HTTPStatusCode"].should.equal(400)
+    ex.response["Error"]["Code"].should.contain("ResourceNotFoundException")
+    ex.response["Error"]["Message"].should.equal(
+        "The account with id '123456789012' does not include a pipeline with the name 'not-existing'"
+    )
+
+    with assert_raises(ClientError) as e:
+        client.tag_resource(
+            resourceArn="arn:aws:codepipeline:us-east-1:123456789012:{}".format(name),
+            tags=[{"key": "aws:key", "value": "value"}],
+        )
+    ex = e.exception
+    ex.operation_name.should.equal("TagResource")
+    ex.response["ResponseMetadata"]["HTTPStatusCode"].should.equal(400)
+    ex.response["Error"]["Code"].should.contain("InvalidTagsException")
+    ex.response["Error"]["Message"].should.equal(
+        "Not allowed to modify system tags. "
+        "System tags start with 'aws:'. "
+        "msg=[Caller is an end user and not allowed to mutate system tags]"
+    )
+
+    with assert_raises(ClientError) as e:
+        client.tag_resource(
+            resourceArn="arn:aws:codepipeline:us-east-1:123456789012:{}".format(name),
+            tags=[
+                {"key": "key-{}".format(i), "value": "value-{}".format(i)}
+                for i in range(50)
+            ],
+        )
+    ex = e.exception
+    ex.operation_name.should.equal("TagResource")
+    ex.response["ResponseMetadata"]["HTTPStatusCode"].should.equal(400)
+    ex.response["Error"]["Code"].should.contain("TooManyTagsException")
+    ex.response["Error"]["Message"].should.equal(
+        "Tag limit exceeded for resource [arn:aws:codepipeline:us-east-1:123456789012:{}].".format(
+            name
+        )
+    )
+
+
 @mock_iam
 def get_role_arn():
     client = boto3.client("iam", region_name="us-east-1")