diff --git a/moto/emr/models.py b/moto/emr/models.py
index 63aadf105..5a34c4d10 100644
--- a/moto/emr/models.py
+++ b/moto/emr/models.py
@@ -146,6 +146,7 @@ class FakeCluster(BaseModel):
         requested_ami_version=None,
         running_ami_version=None,
         custom_ami_id=None,
+        step_concurrency_level=1,
     ):
         self.id = cluster_id or random_cluster_id()
         emr_backend.clusters[self.id] = self
@@ -236,6 +237,7 @@ class FakeCluster(BaseModel):
 
         self.role = job_flow_role or "EMRJobflowDefault"
         self.service_role = service_role
+        self.step_concurrency_level = step_concurrency_level
 
         self.creation_datetime = datetime.now(pytz.utc)
         self.start_datetime = None
@@ -469,6 +471,11 @@ class ElasticMapReduceBackend(BaseBackend):
         )
         return steps[start_idx : start_idx + max_items], marker
 
+    def modify_cluster(self, cluster_id, step_concurrency_level):
+        cluster = self.clusters[cluster_id]
+        cluster.step_concurrency_level = step_concurrency_level
+        return cluster
+
     def modify_instance_groups(self, instance_groups):
         result_groups = []
         for instance_group in instance_groups:
diff --git a/moto/emr/responses.py b/moto/emr/responses.py
index 38a33519c..9ced4569b 100644
--- a/moto/emr/responses.py
+++ b/moto/emr/responses.py
@@ -127,9 +127,6 @@ class ElasticMapReduceResponse(BaseResponse):
         template = self.response_template(DESCRIBE_JOB_FLOWS_TEMPLATE)
         return template.render(clusters=clusters)
 
-    def describe_security_configuration(self):
-        raise NotImplementedError
-
     @generate_boto3_response("DescribeStep")
     def describe_step(self):
         cluster_id = self._get_param("ClusterId")
@@ -185,6 +182,17 @@ class ElasticMapReduceResponse(BaseResponse):
         template = self.response_template(LIST_STEPS_TEMPLATE)
         return template.render(steps=steps, marker=marker)
 
+    @generate_boto3_response("ModifyCluster")
+    def modify_cluster(self):
+        cluster_id = self._get_param("ClusterId")
+        step_concurrency_level = self._get_param("StepConcurrencyLevel")
+        cluster = self.backend.modify_cluster(cluster_id, step_concurrency_level)
+        template = self.response_template(MODIFY_CLUSTER_TEMPLATE)
+        return template.render(cluster=cluster)
+
+    def describe_security_configuration(self):
+        raise NotImplementedError
+
     @generate_boto3_response("ModifyInstanceGroups")
     def modify_instance_groups(self):
         instance_groups = self._get_list_prefix("InstanceGroups.member")
@@ -315,6 +323,10 @@ class ElasticMapReduceResponse(BaseResponse):
                     template="error_json",
                 )
 
+        step_concurrency_level = self._get_param("StepConcurrencyLevel")
+        if step_concurrency_level:
+            kwargs["step_concurrency_level"] = step_concurrency_level
+
         cluster = self.backend.run_job_flow(**kwargs)
 
         applications = self._get_list_prefix("Applications.member")
@@ -591,6 +603,7 @@ DESCRIBE_CLUSTER_TEMPLATE = """<DescribeClusterResponse xmlns="http://elasticmap
       </Tags>
       <TerminationProtected>{{ cluster.termination_protected|lower }}</TerminationProtected>
       <VisibleToAllUsers>{{ cluster.visible_to_all_users|lower }}</VisibleToAllUsers>
+      <StepConcurrencyLevel>{{ cluster.step_concurrency_level }}</StepConcurrencyLevel>
     </Cluster>
   </DescribeClusterResult>
   <ResponseMetadata>
@@ -1075,6 +1088,16 @@ LIST_STEPS_TEMPLATE = """<ListStepsResponse xmlns="http://elasticmapreduce.amazo
   </ResponseMetadata>
 </ListStepsResponse>"""
 
+MODIFY_CLUSTER_TEMPLATE = """<ModifyClusterResponse xmlns="http://elasticmapreduce.amazonaws.com/doc/2009-03-31">
+  <ModifyClusterResult>
+    <StepConcurrencyLevel>{{ cluster.step_concurrency_level }}</StepConcurrencyLevel>
+  </ModifyClusterResult>
+  <ResponseMetadata>
+    <RequestId>0751c837-e78d-4aef-95c9-9c4d29a092ff</RequestId>
+  </ResponseMetadata>
+</ModifyClusterResponse>
+"""
+
 MODIFY_INSTANCE_GROUPS_TEMPLATE = """<ModifyInstanceGroupsResponse xmlns="http://elasticmapreduce.amazonaws.com/doc/2009-03-31">
   <ResponseMetadata>
     <RequestId>2690d7eb-ed86-11dd-9877-6fad448a8419</RequestId>
diff --git a/tests/test_emr/test_emr_boto3.py b/tests/test_emr/test_emr_boto3.py
index 3f577c69a..af6939f80 100644
--- a/tests/test_emr/test_emr_boto3.py
+++ b/tests/test_emr/test_emr_boto3.py
@@ -631,6 +631,36 @@ def test_run_job_flow_with_custom_ami():
     resp["Cluster"]["CustomAmiId"].should.equal("MyEmrCustomAmi")
 
 
+@mock_emr
+def test_run_job_flow_with_step_concurrency():
+    client = boto3.client("emr", region_name="us-east-1")
+    args = deepcopy(run_job_flow_args)
+    args["StepConcurrencyLevel"] = 2
+    cluster_id = client.run_job_flow(**args)["JobFlowId"]
+    resp = client.describe_cluster(ClusterId=cluster_id)["Cluster"]
+    resp["Name"].should.equal(args["Name"])
+    resp["Status"]["State"].should.equal("WAITING")
+    resp["StepConcurrencyLevel"].should.equal(2)
+
+
+@mock_emr
+def test_modify_cluster():
+    client = boto3.client("emr", region_name="us-east-1")
+    args = deepcopy(run_job_flow_args)
+    args["StepConcurrencyLevel"] = 2
+    cluster_id = client.run_job_flow(**args)["JobFlowId"]
+    resp = client.describe_cluster(ClusterId=cluster_id)["Cluster"]
+    resp["Name"].should.equal(args["Name"])
+    resp["Status"]["State"].should.equal("WAITING")
+    resp["StepConcurrencyLevel"].should.equal(2)
+
+    resp = client.modify_cluster(ClusterId=cluster_id, StepConcurrencyLevel=4)
+    resp["StepConcurrencyLevel"].should.equal(4)
+
+    resp = client.describe_cluster(ClusterId=cluster_id)["Cluster"]
+    resp["StepConcurrencyLevel"].should.equal(4)
+
+
 @mock_emr
 def test_set_termination_protection():
     client = boto3.client("emr", region_name="us-east-1")