diff --git a/common/src/main/java/com/netflix/conductor/common/metadata/workflow/IdempotencyStrategy.java b/common/src/main/java/com/netflix/conductor/common/metadata/workflow/IdempotencyStrategy.java
new file mode 100644
index 0000000000..a3d4397253
--- /dev/null
+++ b/common/src/main/java/com/netflix/conductor/common/metadata/workflow/IdempotencyStrategy.java
@@ -0,0 +1,18 @@
+/*
+ * Copyright 2020 Netflix, Inc.
+ * <p>
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package com.netflix.conductor.common.metadata.workflow;
+
+public enum IdempotencyStrategy {
+    FAIL,
+    RETURN_EXISTING
+}
diff --git a/common/src/main/java/com/netflix/conductor/common/metadata/workflow/StartWorkflowRequest.java b/common/src/main/java/com/netflix/conductor/common/metadata/workflow/StartWorkflowRequest.java
index 5112fea6b5..fc99ce84e6 100644
--- a/common/src/main/java/com/netflix/conductor/common/metadata/workflow/StartWorkflowRequest.java
+++ b/common/src/main/java/com/netflix/conductor/common/metadata/workflow/StartWorkflowRequest.java
@@ -57,6 +57,26 @@ public class StartWorkflowRequest {
     @ProtoField(id = 9)
     private String createdBy;
 
+    private String idempotencyKey;
+
+    private IdempotencyStrategy idempotencyStrategy;
+
+    public String getIdempotencyKey() {
+        return idempotencyKey;
+    }
+
+    public void setIdempotencyKey(String idempotencyKey) {
+        this.idempotencyKey = idempotencyKey;
+    }
+
+    public IdempotencyStrategy getIdempotencyStrategy() {
+        return idempotencyStrategy;
+    }
+
+    public void setIdempotencyStrategy(IdempotencyStrategy idempotencyStrategy) {
+        this.idempotencyStrategy = idempotencyStrategy;
+    }
+
     public String getName() {
         return name;
     }
diff --git a/common/src/main/java/com/netflix/conductor/common/run/Workflow.java b/common/src/main/java/com/netflix/conductor/common/run/Workflow.java
index fa56d43e43..50ebd78cf5 100644
--- a/common/src/main/java/com/netflix/conductor/common/run/Workflow.java
+++ b/common/src/main/java/com/netflix/conductor/common/run/Workflow.java
@@ -126,6 +126,16 @@ public boolean isSuccessful() {
     @ProtoField(id = 25)
     private List<Workflow> history = new LinkedList<>();
 
+    private String idempotencyKey;
+
+    public String getIdempotencyKey() {
+        return idempotencyKey;
+    }
+
+    public void setIdempotencyKey(String idempotencyKey) {
+        this.idempotencyKey = idempotencyKey;
+    }
+
     public List<Workflow> getHistory() {
         return history;
     }
diff --git a/common/src/main/java/com/netflix/conductor/common/validation/ErrorResponse.java b/common/src/main/java/com/netflix/conductor/common/validation/ErrorResponse.java
index 5ed6256e1d..6c247aca11 100644
--- a/common/src/main/java/com/netflix/conductor/common/validation/ErrorResponse.java
+++ b/common/src/main/java/com/netflix/conductor/common/validation/ErrorResponse.java
@@ -13,6 +13,7 @@
 package com.netflix.conductor.common.validation;
 
 import java.util.List;
+import java.util.Map;
 
 public class ErrorResponse {
 
@@ -23,6 +24,16 @@ public class ErrorResponse {
     private boolean retryable;
     private List<ValidationError> validationErrors;
 
+    private Map<String, Object> metadata;
+
+    public Map<String, Object> getMetadata() {
+        return metadata;
+    }
+
+    public void setMetadata(Map<String, Object> metadata) {
+        this.metadata = metadata;
+    }
+
     public int getStatus() {
         return status;
     }
diff --git a/core/src/main/java/com/netflix/conductor/core/exception/ApplicationException.java b/core/src/main/java/com/netflix/conductor/core/exception/ApplicationException.java
index f1a086d403..e0aee23526 100644
--- a/core/src/main/java/com/netflix/conductor/core/exception/ApplicationException.java
+++ b/core/src/main/java/com/netflix/conductor/core/exception/ApplicationException.java
@@ -39,6 +39,16 @@ public int getStatusCode() {
         }
     }
 
+    public Map<String, Object> getMetadata() {
+        return metadata;
+    }
+
+    public void setMetadata(Map<String, Object> metadata) {
+        this.metadata = metadata;
+    }
+
+    private Map<String, Object> metadata;
+
     private final Code code;
 
     public boolean isRetryable() {
@@ -64,6 +74,12 @@ public ApplicationException(Code code, String message) {
         this.code = code;
     }
 
+    public ApplicationException(Code code, String message, Map<String, Object> metadata) {
+        super(message);
+        this.code = code;
+        this.metadata = metadata;
+    }
+
     public int getHttpStatusCode() {
         return this.code.getStatusCode();
     }
diff --git a/core/src/main/java/com/netflix/conductor/model/WorkflowModel.java b/core/src/main/java/com/netflix/conductor/model/WorkflowModel.java
index 613a01870a..da96269331 100644
--- a/core/src/main/java/com/netflix/conductor/model/WorkflowModel.java
+++ b/core/src/main/java/com/netflix/conductor/model/WorkflowModel.java
@@ -102,6 +102,7 @@ public boolean isSuccessful() {
     private String failedTaskId;
 
     private Status previousStatus;
+    private String idempotencyKey;
 
     private List<WorkflowModel> history = new LinkedList<>();
 
@@ -449,6 +450,14 @@ public TaskModel getTaskByRefName(String refName) {
         return found.getLast();
     }
 
+    public String getIdempotencyKey() {
+        return idempotencyKey;
+    }
+
+    public void setIdempotencyKey(String idempotencyKey) {
+        this.idempotencyKey = idempotencyKey;
+    }
+
     public void externalizeInput(String path) {
         this.inputPayload = this.input;
         this.input = new HashMap<>();