diff --git a/moto/kms/models.py b/moto/kms/models.py
--- a/moto/kms/models.py
+++ b/moto/kms/models.py
@@ -3,8 +3,8 @@
 from collections import defaultdict
 from datetime import datetime, timedelta
 
-from moto.core import get_account_id, BaseBackend, CloudFormationModel
-from moto.core.utils import unix_time, BackendDict
+from moto.core import get_account_id, BaseBackend, BaseModel, CloudFormationModel
+from moto.core.utils import get_random_hex, unix_time, BackendDict
 from moto.utilities.tagging_service import TaggingService
 from moto.core.exceptions import JsonRESTError
 
@@ -17,6 +17,37 @@
 )
 
 
+class Grant(BaseModel):
+    def __init__(
+        self,
+        key_id,
+        name,
+        grantee_principal,
+        operations,
+        constraints,
+        retiring_principal,
+    ):
+        self.key_id = key_id
+        self.name = name
+        self.grantee_principal = grantee_principal
+        self.retiring_principal = retiring_principal
+        self.operations = operations
+        self.constraints = constraints
+        self.id = get_random_hex()
+        self.token = get_random_hex()
+
+    def to_json(self):
+        return {
+            "KeyId": self.key_id,
+            "GrantId": self.id,
+            "Name": self.name,
+            "GranteePrincipal": self.grantee_principal,
+            "RetiringPrincipal": self.retiring_principal,
+            "Operations": self.operations,
+            "Constraints": self.constraints,
+        }
+
+
 class Key(CloudFormationModel):
     def __init__(
         self, policy, key_usage, customer_master_key_spec, description, region
@@ -37,6 +68,46 @@ def __init__(
         self.key_manager = "CUSTOMER"
         self.customer_master_key_spec = customer_master_key_spec or "SYMMETRIC_DEFAULT"
 
+        self.grants = dict()
+
+    def add_grant(
+        self, name, grantee_principal, operations, constraints, retiring_principal
+    ) -> Grant:
+        grant = Grant(
+            self.id,
+            name,
+            grantee_principal,
+            operations,
+            constraints=constraints,
+            retiring_principal=retiring_principal,
+        )
+        self.grants[grant.id] = grant
+        return grant
+
+    def list_grants(self, grant_id) -> [Grant]:
+        grant_ids = [grant_id] if grant_id else self.grants.keys()
+        return [grant for _id, grant in self.grants.items() if _id in grant_ids]
+
+    def list_retirable_grants(self, retiring_principal) -> [Grant]:
+        return [
+            grant
+            for grant in self.grants.values()
+            if grant.retiring_principal == retiring_principal
+        ]
+
+    def revoke_grant(self, grant_id) -> None:
+        self.grants.pop(grant_id, None)
+
+    def retire_grant(self, grant_id) -> None:
+        self.grants.pop(grant_id, None)
+
+    def retire_grant_by_token(self, grant_token) -> None:
+        self.grants = {
+            _id: grant
+            for _id, grant in self.grants.items()
+            if grant.token != grant_token
+        }
+
     def generate_default_policy(self):
         return json.dumps(
             {
@@ -214,7 +285,7 @@ def delete_key(self, key_id):
 
             return self.keys.pop(key_id)
 
-    def describe_key(self, key_id):
+    def describe_key(self, key_id) -> Key:
         # allow the different methods (alias, ARN :key/, keyId, ARN alias) to
         # describe key not just KeyId
         key_id = self.get_key_id(key_id)
@@ -410,5 +481,46 @@ def untag_resource(self, key_id_or_arn, tag_names):
             "The request was rejected because the specified entity or resource could not be found.",
         )
 
+    def create_grant(
+        self,
+        key_id,
+        grantee_principal,
+        operations,
+        name,
+        constraints,
+        retiring_principal,
+    ):
+        key = self.describe_key(key_id)
+        grant = key.add_grant(
+            name,
+            grantee_principal,
+            operations,
+            constraints=constraints,
+            retiring_principal=retiring_principal,
+        )
+        return grant.id, grant.token
+
+    def list_grants(self, key_id, grant_id) -> [Grant]:
+        key = self.describe_key(key_id)
+        return key.list_grants(grant_id)
+
+    def list_retirable_grants(self, retiring_principal):
+        grants = []
+        for key in self.keys.values():
+            grants.extend(key.list_retirable_grants(retiring_principal))
+        return grants
+
+    def revoke_grant(self, key_id, grant_id) -> None:
+        key = self.describe_key(key_id)
+        key.revoke_grant(grant_id)
+
+    def retire_grant(self, key_id, grant_id, grant_token) -> None:
+        if grant_token:
+            for key in self.keys.values():
+                key.retire_grant_by_token(grant_token)
+        else:
+            key = self.describe_key(key_id)
+            key.retire_grant(grant_id)
+
 
 kms_backends = BackendDict(KmsBackend, "kms")
diff --git a/moto/kms/responses.py b/moto/kms/responses.py
--- a/moto/kms/responses.py
+++ b/moto/kms/responses.py
@@ -284,6 +284,64 @@ def list_aliases(self):
 
         return json.dumps({"Truncated": False, "Aliases": response_aliases})
 
+    def create_grant(self):
+        key_id = self.parameters.get("KeyId")
+        grantee_principal = self.parameters.get("GranteePrincipal")
+        retiring_principal = self.parameters.get("RetiringPrincipal")
+        operations = self.parameters.get("Operations")
+        name = self.parameters.get("Name")
+        constraints = self.parameters.get("Constraints")
+
+        grant_id, grant_token = self.kms_backend.create_grant(
+            key_id,
+            grantee_principal,
+            operations,
+            name,
+            constraints=constraints,
+            retiring_principal=retiring_principal,
+        )
+        return json.dumps({"GrantId": grant_id, "GrantToken": grant_token})
+
+    def list_grants(self):
+        key_id = self.parameters.get("KeyId")
+        grant_id = self.parameters.get("GrantId")
+
+        grants = self.kms_backend.list_grants(key_id=key_id, grant_id=grant_id)
+        return json.dumps(
+            {
+                "Grants": [gr.to_json() for gr in grants],
+                "GrantCount": len(grants),
+                "Truncated": False,
+            }
+        )
+
+    def list_retirable_grants(self):
+        retiring_principal = self.parameters.get("RetiringPrincipal")
+
+        grants = self.kms_backend.list_retirable_grants(retiring_principal)
+        return json.dumps(
+            {
+                "Grants": [gr.to_json() for gr in grants],
+                "GrantCount": len(grants),
+                "Truncated": False,
+            }
+        )
+
+    def revoke_grant(self):
+        key_id = self.parameters.get("KeyId")
+        grant_id = self.parameters.get("GrantId")
+
+        self.kms_backend.revoke_grant(key_id, grant_id)
+        return "{}"
+
+    def retire_grant(self):
+        key_id = self.parameters.get("KeyId")
+        grant_id = self.parameters.get("GrantId")
+        grant_token = self.parameters.get("GrantToken")
+
+        self.kms_backend.retire_grant(key_id, grant_id, grant_token)
+        return "{}"
+
     def enable_key_rotation(self):
         """https://docs.aws.amazon.com/kms/latest/APIReference/API_EnableKeyRotation.html"""
         key_id = self.parameters.get("KeyId")

diff --git a/tests/terraformtests/terraform-tests.success.txt b/tests/terraformtests/terraform-tests.success.txt
--- a/tests/terraformtests/terraform-tests.success.txt
+++ b/tests/terraformtests/terraform-tests.success.txt
@@ -109,6 +109,12 @@ iot:
   - TestAccIoTEndpointDataSource
 kms:
   - TestAccKMSAlias
+  - TestAccKMSGrant_arn
+  - TestAccKMSGrant_asymmetricKey
+  - TestAccKMSGrant_basic
+  - TestAccKMSGrant_bare
+  - TestAccKMSGrant_withConstraints
+  - TestAccKMSGrant_withRetiringPrincipal
   - TestAccKMSKey_Policy_basic
   - TestAccKMSKey_Policy_iamRole
   - TestAccKMSKey_Policy_iamRoleOrder
diff --git a/tests/test_kms/test_kms_grants.py b/tests/test_kms/test_kms_grants.py
new file mode 100644
--- /dev/null
+++ b/tests/test_kms/test_kms_grants.py
@@ -0,0 +1,194 @@
+import boto3
+import sure  # noqa # pylint: disable=unused-import
+
+from moto import mock_kms
+from moto.core import ACCOUNT_ID
+
+
+grantee_principal = (
+    f"arn:aws:iam::{ACCOUNT_ID}:role/service-role/tf-acc-test-7071877926602081451"
+)
+
+
+@mock_kms
+def test_create_grant():
+    client = boto3.client("kms", region_name="us-east-1")
+    key_id = client.create_key(Policy="my policy")["KeyMetadata"]["KeyId"]
+
+    resp = client.create_grant(
+        KeyId=key_id,
+        GranteePrincipal=grantee_principal,
+        Operations=["DECRYPT"],
+        Name="testgrant",
+    )
+    resp.should.have.key("GrantId")
+    resp.should.have.key("GrantToken")
+
+
+@mock_kms
+def test_list_grants():
+    client = boto3.client("kms", region_name="us-east-1")
+    key_id = client.create_key(Policy="my policy")["KeyMetadata"]["KeyId"]
+
+    client.list_grants(KeyId=key_id).should.have.key("Grants").equals([])
+
+    grant_id1 = client.create_grant(
+        KeyId=key_id,
+        GranteePrincipal=grantee_principal,
+        Operations=["DECRYPT"],
+        Name="testgrant",
+    )["GrantId"]
+
+    grant_id2 = client.create_grant(
+        KeyId=key_id,
+        GranteePrincipal=grantee_principal,
+        Operations=["DECRYPT", "ENCRYPT"],
+        Constraints={"EncryptionContextSubset": {"baz": "kaz", "foo": "bar"}},
+    )["GrantId"]
+
+    # List all
+    grants = client.list_grants(KeyId=key_id)["Grants"]
+    grants.should.have.length_of(2)
+    grant_1 = [grant for grant in grants if grant["GrantId"] == grant_id1][0]
+    grant_2 = [grant for grant in grants if grant["GrantId"] == grant_id2][0]
+
+    grant_1.should.have.key("KeyId").equals(key_id)
+    grant_1.should.have.key("GrantId").equals(grant_id1)
+    grant_1.should.have.key("Name").equals("testgrant")
+    grant_1.should.have.key("GranteePrincipal").equals(grantee_principal)
+    grant_1.should.have.key("Operations").equals(["DECRYPT"])
+
+    grant_2.should.have.key("KeyId").equals(key_id)
+    grant_2.should.have.key("GrantId").equals(grant_id2)
+    grant_2.shouldnt.have.key("Name")
+    grant_2.should.have.key("GranteePrincipal").equals(grantee_principal)
+    grant_2.should.have.key("Operations").equals(["DECRYPT", "ENCRYPT"])
+    grant_2.should.have.key("Constraints").equals(
+        {"EncryptionContextSubset": {"baz": "kaz", "foo": "bar"}}
+    )
+
+    # List by grant_id
+    grants = client.list_grants(KeyId=key_id, GrantId=grant_id2)["Grants"]
+    grants.should.have.length_of(1)
+    grants[0]["GrantId"].should.equal(grant_id2)
+
+    # List by unknown grant_id
+    grants = client.list_grants(KeyId=key_id, GrantId="unknown")["Grants"]
+    grants.should.have.length_of(0)
+
+
+@mock_kms
+def test_list_retirable_grants():
+    client = boto3.client("kms", region_name="us-east-1")
+    key_id1 = client.create_key(Policy="my policy")["KeyMetadata"]["KeyId"]
+    key_id2 = client.create_key(Policy="my policy")["KeyMetadata"]["KeyId"]
+
+    client.create_grant(
+        KeyId=key_id1,
+        GranteePrincipal=grantee_principal,
+        Operations=["DECRYPT"],
+    )
+
+    client.create_grant(
+        KeyId=key_id1,
+        GranteePrincipal=grantee_principal,
+        RetiringPrincipal="sth else",
+        Operations=["DECRYPT"],
+    )
+
+    client.create_grant(
+        KeyId=key_id2,
+        GranteePrincipal=grantee_principal,
+        Operations=["DECRYPT"],
+    )
+
+    grant2_key2 = client.create_grant(
+        KeyId=key_id2,
+        GranteePrincipal=grantee_principal,
+        RetiringPrincipal="principal",
+        Operations=["DECRYPT"],
+    )["GrantId"]
+
+    # List only the grants from the retiring principal
+    grants = client.list_retirable_grants(RetiringPrincipal="principal")["Grants"]
+    grants.should.have.length_of(1)
+    grants[0]["KeyId"].should.equal(key_id2)
+    grants[0]["GrantId"].should.equal(grant2_key2)
+
+
+@mock_kms
+def test_revoke_grant():
+
+    client = boto3.client("kms", region_name="us-east-1")
+    key_id = client.create_key(Policy="my policy")["KeyMetadata"]["KeyId"]
+
+    client.list_grants(KeyId=key_id).should.have.key("Grants").equals([])
+
+    grant_id = client.create_grant(
+        KeyId=key_id,
+        GranteePrincipal=grantee_principal,
+        Operations=["DECRYPT"],
+        Name="testgrant",
+    )["GrantId"]
+
+    client.revoke_grant(KeyId=key_id, GrantId=grant_id)
+
+    client.list_grants(KeyId=key_id)["Grants"].should.have.length_of(0)
+
+
+@mock_kms
+def test_revoke_grant_by_token():
+
+    client = boto3.client("kms", region_name="us-east-1")
+    key_id = client.create_key(Policy="my policy")["KeyMetadata"]["KeyId"]
+
+    client.list_grants(KeyId=key_id).should.have.key("Grants").equals([])
+
+    grant_id = client.create_grant(
+        KeyId=key_id,
+        GranteePrincipal=grantee_principal,
+        Operations=["DECRYPT"],
+        Name="testgrant",
+    )["GrantId"]
+
+    client.revoke_grant(KeyId=key_id, GrantId=grant_id)
+
+    client.list_grants(KeyId=key_id)["Grants"].should.have.length_of(0)
+
+
+@mock_kms
+def test_retire_grant_by_token():
+
+    client = boto3.client("kms", region_name="us-east-1")
+    key_id = client.create_key(Policy="my policy")["KeyMetadata"]["KeyId"]
+
+    for idx in range(0, 3):
+        grant_token = client.create_grant(
+            KeyId=key_id,
+            GranteePrincipal=grantee_principal,
+            Operations=["DECRYPT"],
+            Name=f"testgrant{idx}",
+        )["GrantToken"]
+
+    client.retire_grant(GrantToken=grant_token)
+
+    client.list_grants(KeyId=key_id)["Grants"].should.have.length_of(2)
+
+
+@mock_kms
+def test_retire_grant_by_grant_id():
+
+    client = boto3.client("kms", region_name="us-east-1")
+    key_id = client.create_key(Policy="my policy")["KeyMetadata"]["KeyId"]
+
+    for idx in range(0, 3):
+        grant_id = client.create_grant(
+            KeyId=key_id,
+            GranteePrincipal=grantee_principal,
+            Operations=["DECRYPT"],
+            Name=f"testgrant{idx}",
+        )["GrantId"]
+
+    client.retire_grant(KeyId=key_id, GrantId=grant_id)
+
+    client.list_grants(KeyId=key_id)["Grants"].should.have.length_of(2)

Feature Request: KMS supports grants api
- [ ] create-grant
- [ ] list-grants
- [ ] list-retirable-grants
- [ ] retire-grant
- [ ] revoke-grant

tests/test_kms/test_kms_grants.py::test_list_retirable_grants tests/test_kms/test_kms_grants.py::test_list_grants tests/test_kms/test_kms_grants.py::test_create_grant tests/test_kms/test_kms_grants.py::test_retire_grant_by_grant_id tests/test_kms/test_kms_grants.py::test_revoke_grant_by_token tests/test_kms/test_kms_grants.py::test_retire_grant_by_token tests/test_kms/test_kms_grants.py::test_revoke_grant