diff --git a/moto/swf/models/__init__.py b/moto/swf/models/__init__.py
index a206e3e78..27f56a711 100644
--- a/moto/swf/models/__init__.py
+++ b/moto/swf/models/__init__.py
@@ -160,7 +160,7 @@ class SWFBackend(BaseBackend):
         self._check_string(run_id)
         self._check_string(workflow_id)
         domain = self._get_domain(domain_name)
-        return domain.get_workflow_execution(run_id, workflow_id)
+        return domain.get_workflow_execution(workflow_id, run_id=run_id)
 
     def poll_for_decision_task(self, domain_name, task_list, identity=None):
         self._check_string(domain_name)
@@ -198,7 +198,7 @@ class SWFBackend(BaseBackend):
         self._check_string(task_list)
         domain = self._get_domain(domain_name)
         count = 0
-        for _, wfe in domain.workflow_executions.iteritems():
+        for wfe in domain.workflow_executions:
             if wfe.task_list == task_list:
                 count += wfe.open_counts["openDecisionTasks"]
         return count
@@ -211,7 +211,7 @@ class SWFBackend(BaseBackend):
         # let's find decision task
         decision_task = None
         for domain in self.domains:
-            for _, wfe in domain.workflow_executions.iteritems():
+            for wfe in domain.workflow_executions:
                 for dt in wfe.decision_tasks:
                     if dt.task_token == task_token:
                         decision_task = dt
@@ -301,7 +301,7 @@ class SWFBackend(BaseBackend):
     def _find_activity_task_from_token(self, task_token):
         activity_task = None
         for domain in self.domains:
-            for _, wfe in domain.workflow_executions.iteritems():
+            for wfe in domain.workflow_executions:
                 for task in wfe.activity_tasks:
                     if task.task_token == task_token:
                         activity_task = task
@@ -352,6 +352,18 @@ class SWFBackend(BaseBackend):
         wfe = activity_task.workflow_execution
         wfe.fail_activity_task(activity_task.task_token, reason=reason, details=details)
 
+    def terminate_workflow_execution(self, domain_name, workflow_id, child_policy=None,
+                                     details=None, reason=None, run_id=None):
+        self._check_string(domain_name)
+        self._check_string(workflow_id)
+        self._check_none_or_string(child_policy)
+        self._check_none_or_string(details)
+        self._check_none_or_string(reason)
+        self._check_none_or_string(run_id)
+        domain = self._get_domain(domain_name)
+        wfe = domain.get_workflow_execution(workflow_id, run_id=run_id, raise_if_closed=True)
+        wfe.terminate(child_policy=child_policy, details=details, reason=reason)
+
 
 swf_backends = {}
 for region in boto.swf.regions():
diff --git a/moto/swf/models/domain.py b/moto/swf/models/domain.py
index d04a41841..9caf307f4 100644
--- a/moto/swf/models/domain.py
+++ b/moto/swf/models/domain.py
@@ -22,7 +22,7 @@ class Domain(object):
         # that against SWF API) ; hence the storage method as a dict
         # of "workflow_id (client determined)" => WorkflowExecution()
         # here.
-        self.workflow_executions = {}
+        self.workflow_executions = []
         self.activity_task_lists = {}
         self.decision_task_lists = {}
 
@@ -71,18 +71,32 @@ class Domain(object):
 
     def add_workflow_execution(self, workflow_execution):
         _id = workflow_execution.workflow_id
-        if self.workflow_executions.get(_id):
+        # TODO: handle this better: this should raise ONLY if there's an OPEN wfe with this ID
+        if any(wfe.workflow_id == _id for wfe in self.workflow_executions):
             raise SWFWorkflowExecutionAlreadyStartedFault()
-        self.workflow_executions[_id] = workflow_execution
+        self.workflow_executions.append(workflow_execution)
 
-    def get_workflow_execution(self, run_id, workflow_id):
-        wfe = self.workflow_executions.get(workflow_id)
-        if not wfe or wfe.run_id != run_id:
-            raise SWFUnknownResourceFault(
-                "execution",
-                "WorkflowExecution=[workflowId={}, runId={}]".format(
-                    workflow_id, run_id
+    def get_workflow_execution(self, workflow_id, run_id=None, raise_if_closed=False):
+        if run_id:
+            _all = [w for w in self.workflow_executions
+                    if w.workflow_id == workflow_id and w.run_id == run_id]
+        else:
+            _all = [w for w in self.workflow_executions
+                    if w.workflow_id == workflow_id and w.execution_status == "OPEN"]
+        wfe = _all[0] if _all else None
+        if raise_if_closed and wfe and wfe.execution_status == "CLOSED":
+            wfe = None
+        if run_id:
+            if not wfe or wfe.run_id != run_id:
+                raise SWFUnknownResourceFault(
+                    "execution",
+                    "WorkflowExecution=[workflowId={}, runId={}]".format(
+                        workflow_id, run_id
+                    )
                 )
+        elif not wfe:
+            raise SWFUnknownResourceFault(
+                "execution, workflowId = {}".format(workflow_id)
             )
         return wfe
 
diff --git a/moto/swf/models/history_event.py b/moto/swf/models/history_event.py
index 798cc810c..eb3c1f795 100644
--- a/moto/swf/models/history_event.py
+++ b/moto/swf/models/history_event.py
@@ -132,6 +132,17 @@ class HistoryEvent(object):
             if hasattr(self, "details") and self.details is not None:
                 hsh["details"] = self.details
             return hsh
+        elif self.event_type == "WorkflowExecutionTerminated":
+            hsh = {
+                "childPolicy": self.child_policy,
+            }
+            if self.cause:
+                hsh["cause"] = self.cause
+            if self.details:
+                hsh["details"] = self.details
+            if self.reason:
+                hsh["reason"] = self.reason
+            return hsh
         else:
             raise NotImplementedError(
                 "HistoryEvent does not implement attributes for type '{}'".format(self.event_type)
diff --git a/moto/swf/models/workflow_execution.py b/moto/swf/models/workflow_execution.py
index 40efab156..10d134dca 100644
--- a/moto/swf/models/workflow_execution.py
+++ b/moto/swf/models/workflow_execution.py
@@ -50,6 +50,7 @@ class WorkflowExecution(object):
         # TODO: check valid values among:
         # COMPLETED | FAILED | CANCELED | TERMINATED | CONTINUED_AS_NEW | TIMED_OUT
         # TODO: implement them all
+        self.close_cause = None
         self.close_status = None
         self.close_timestamp = None
         self.execution_status = "OPEN"
@@ -467,3 +468,21 @@ class WorkflowExecution(object):
         self.open_counts["openActivityTasks"] -= 1
         # TODO: ensure we don't schedule multiple decisions at the same time!
         self.schedule_decision_task()
+
+    def terminate(self, child_policy=None, details=None, reason=None):
+        # TODO: handle child policy for child workflows here
+        # TODO: handle cause="CHILD_POLICY_APPLIED"
+        # Until this, we set cause manually to "OPERATOR_INITIATED"
+        cause = "OPERATOR_INITIATED"
+        if not child_policy:
+            child_policy = self.child_policy
+        self._add_event(
+            "WorkflowExecutionTerminated",
+            cause=cause,
+            child_policy=child_policy,
+            details=details,
+            reason=reason,
+        )
+        self.execution_status = "CLOSED"
+        self.close_status = "TERMINATED"
+        self.close_cause = "OPERATOR_INITIATED"
diff --git a/moto/swf/responses.py b/moto/swf/responses.py
index c90fd5d8d..ffadc73f2 100644
--- a/moto/swf/responses.py
+++ b/moto/swf/responses.py
@@ -287,3 +287,16 @@ class SWFResponse(BaseResponse):
             task_token, reason=reason, details=details
         )
         return ""
+
+    def terminate_workflow_execution(self):
+        domain_name = self._params["domain"]
+        workflow_id = self._params["workflowId"]
+        child_policy = self._params.get("childPolicy")
+        details = self._params.get("details")
+        reason = self._params.get("reason")
+        run_id = self._params.get("runId")
+        self.swf_backend.terminate_workflow_execution(
+            domain_name, workflow_id, child_policy=child_policy,
+            details=details, reason=reason, run_id=run_id
+        )
+        return ""
diff --git a/tests/test_swf/models/test_domain.py b/tests/test_swf/models/test_domain.py
index 5d2982e10..215cbace0 100644
--- a/tests/test_swf/models/test_domain.py
+++ b/tests/test_swf/models/test_domain.py
@@ -1,8 +1,17 @@
+from collections import namedtuple
 from sure import expect
 
+from moto.swf.exceptions import SWFUnknownResourceFault
 from moto.swf.models import Domain
 
 
+# Fake WorkflowExecution for tests purposes
+WorkflowExecution = namedtuple(
+    "WorkflowExecution",
+    ["workflow_id", "run_id", "execution_status"]
+)
+
+
 def test_domain_short_dict_representation():
     domain = Domain("foo", "52")
     domain.to_short_dict().should.equal({"name":"foo", "status":"REGISTERED"})
@@ -46,3 +55,45 @@ def test_domain_decision_tasks():
     domain.add_to_decision_task_list("foo", "bar")
     domain.add_to_decision_task_list("other", "baz")
     domain.decision_tasks.should.equal(["bar", "baz"])
+
+def test_domain_get_workflow_execution():
+    domain = Domain("my-domain", "60")
+
+    wfe1 = WorkflowExecution(workflow_id="wf-id-1", run_id="run-id-1", execution_status="OPEN")
+    wfe2 = WorkflowExecution(workflow_id="wf-id-1", run_id="run-id-2", execution_status="CLOSED")
+    wfe3 = WorkflowExecution(workflow_id="wf-id-2", run_id="run-id-3", execution_status="OPEN")
+    wfe4 = WorkflowExecution(workflow_id="wf-id-3", run_id="run-id-4", execution_status="CLOSED")
+    domain.workflow_executions = [wfe1, wfe2, wfe3, wfe4]
+
+    # get workflow execution through workflow_id and run_id
+    domain.get_workflow_execution("wf-id-1", run_id="run-id-1").should.equal(wfe1)
+    domain.get_workflow_execution("wf-id-1", run_id="run-id-2").should.equal(wfe2)
+    domain.get_workflow_execution("wf-id-3", run_id="run-id-4").should.equal(wfe4)
+    domain.get_workflow_execution.when.called_with(
+        "wf-id-1", run_id="non-existent"
+    ).should.throw(
+        SWFUnknownResourceFault,
+        "Unknown execution: WorkflowExecution=[workflowId=wf-id-1, runId=non-existent]"
+    )
+
+    # get OPEN workflow execution by default if no run_id
+    domain.get_workflow_execution("wf-id-1").should.equal(wfe1)
+    domain.get_workflow_execution.when.called_with(
+        "wf-id-3"
+    ).should.throw(
+        SWFUnknownResourceFault, "Unknown execution, workflowId = wf-id-3"
+    )
+    domain.get_workflow_execution.when.called_with(
+        "wf-id-non-existent"
+    ).should.throw(
+        SWFUnknownResourceFault, "Unknown execution, workflowId = wf-id-non-existent"
+    )
+
+    # raise_if_closed attribute
+    domain.get_workflow_execution("wf-id-1", run_id="run-id-1", raise_if_closed=True).should.equal(wfe1)
+    domain.get_workflow_execution.when.called_with(
+        "wf-id-3", run_id="run-id-4", raise_if_closed=True
+    ).should.throw(
+        SWFUnknownResourceFault,
+        "Unknown execution: WorkflowExecution=[workflowId=wf-id-3, runId=run-id-4]"
+    )
diff --git a/tests/test_swf/models/test_workflow_execution.py b/tests/test_swf/models/test_workflow_execution.py
index 21f7c5448..ced636969 100644
--- a/tests/test_swf/models/test_workflow_execution.py
+++ b/tests/test_swf/models/test_workflow_execution.py
@@ -379,3 +379,18 @@ def test_complete_activity_task():
 
     wfe.open_counts["openActivityTasks"].should.equal(0)
     wfe.open_counts["openDecisionTasks"].should.equal(1)
+
+def test_terminate():
+    wfe = make_workflow_execution()
+    wfe.schedule_decision_task()
+    wfe.terminate()
+
+    wfe.execution_status.should.equal("CLOSED")
+    wfe.close_status.should.equal("TERMINATED")
+    wfe.close_cause.should.equal("OPERATOR_INITIATED")
+    wfe.open_counts["openDecisionTasks"].should.equal(1)
+
+    last_event = wfe.events()[-1]
+    last_event.event_type.should.equal("WorkflowExecutionTerminated")
+    # take default child_policy if not provided (as here)
+    last_event.child_policy.should.equal("ABANDON")
diff --git a/tests/test_swf/responses/test_activity_tasks.py b/tests/test_swf/responses/test_activity_tasks.py
index 13825f856..3c7f82b5e 100644
--- a/tests/test_swf/responses/test_activity_tasks.py
+++ b/tests/test_swf/responses/test_activity_tasks.py
@@ -111,7 +111,7 @@ def test_respond_activity_task_completed_on_closed_workflow_execution():
     activity_token = conn.poll_for_activity_task("test-domain", "activity-task-list")["taskToken"]
 
     # bad: we're closing workflow execution manually, but endpoints are not coded for now..
-    wfe = swf_backend.domains[0].workflow_executions.values()[0]
+    wfe = swf_backend.domains[0].workflow_executions[-1]
     wfe.execution_status = "CLOSED"
     # /bad
 
diff --git a/tests/test_swf/responses/test_decision_tasks.py b/tests/test_swf/responses/test_decision_tasks.py
index 64f51d30b..9510b31fd 100644
--- a/tests/test_swf/responses/test_decision_tasks.py
+++ b/tests/test_swf/responses/test_decision_tasks.py
@@ -123,7 +123,7 @@ def test_respond_decision_task_completed_on_close_workflow_execution():
     task_token = resp["taskToken"]
 
     # bad: we're closing workflow execution manually, but endpoints are not coded for now..
-    wfe = swf_backend.domains[0].workflow_executions.values()[0]
+    wfe = swf_backend.domains[0].workflow_executions[-1]
     wfe.execution_status = "CLOSED"
     # /bad
 
diff --git a/tests/test_swf/responses/test_workflow_executions.py b/tests/test_swf/responses/test_workflow_executions.py
index 1b8d599f9..f4125f77c 100644
--- a/tests/test_swf/responses/test_workflow_executions.py
+++ b/tests/test_swf/responses/test_workflow_executions.py
@@ -100,3 +100,64 @@ def test_get_workflow_execution_history_on_non_existent_workflow_execution():
     conn.get_workflow_execution_history.when.called_with(
         "test-domain", "wrong-run-id", "wrong-workflow-id"
     ).should.throw(SWFUnknownResourceFault)
+
+
+# TerminateWorkflowExecution endpoint
+@mock_swf
+def test_terminate_workflow_execution():
+    conn = setup_swf_environment()
+    run_id = conn.start_workflow_execution(
+        "test-domain", "uid-abcd1234", "test-workflow", "v1.0"
+    )["runId"]
+
+    resp = conn.terminate_workflow_execution("test-domain", "uid-abcd1234",
+                                             details="some details",
+                                             reason="a more complete reason",
+                                             run_id=run_id)
+    resp.should.be.none
+
+    resp = conn.get_workflow_execution_history("test-domain", run_id, "uid-abcd1234")
+    evt = resp["events"][-1]
+    evt["eventType"].should.equal("WorkflowExecutionTerminated")
+    attrs = evt["workflowExecutionTerminatedEventAttributes"]
+    attrs["details"].should.equal("some details")
+    attrs["reason"].should.equal("a more complete reason")
+    attrs["cause"].should.equal("OPERATOR_INITIATED")
+
+@mock_swf
+def test_terminate_workflow_execution_with_wrong_workflow_or_run_id():
+    conn = setup_swf_environment()
+    run_id = conn.start_workflow_execution(
+        "test-domain", "uid-abcd1234", "test-workflow", "v1.0"
+    )["runId"]
+
+    # terminate workflow execution
+    resp = conn.terminate_workflow_execution("test-domain", "uid-abcd1234")
+
+    # already closed, with run_id
+    conn.terminate_workflow_execution.when.called_with(
+        "test-domain", "uid-abcd1234", run_id=run_id
+    ).should.throw(
+        SWFUnknownResourceFault, "WorkflowExecution=[workflowId=uid-abcd1234, runId="
+    )
+
+    # already closed, without run_id
+    conn.terminate_workflow_execution.when.called_with(
+        "test-domain", "uid-abcd1234"
+    ).should.throw(
+        SWFUnknownResourceFault, "Unknown execution, workflowId = uid-abcd1234"
+    )
+
+    # wrong workflow id
+    conn.terminate_workflow_execution.when.called_with(
+        "test-domain", "uid-non-existent"
+    ).should.throw(
+        SWFUnknownResourceFault, "Unknown execution, workflowId = uid-non-existent"
+    )
+
+    # wrong run_id
+    conn.terminate_workflow_execution.when.called_with(
+        "test-domain", "uid-abcd1234", run_id="foo"
+    ).should.throw(
+        SWFUnknownResourceFault, "WorkflowExecution=[workflowId=uid-abcd1234, runId="
+    )