diff --git a/src/sprites/rendered-target.js b/src/sprites/rendered-target.js
index 2a6a0f7d3..aa1963480 100644
--- a/src/sprites/rendered-target.js
+++ b/src/sprites/rendered-target.js
@@ -408,6 +408,17 @@ class RenderedTarget extends Target {
         this.sprite.costumes.push(costumeObject);
     }
 
+    /**
+     * Add a costume at the given index, taking care to avoid duplicate names.
+     * @param {!object} costumeObject Object representing the costume.
+     * @param {!int} index Index at which to add costume
+     */
+    addCostumeAt (costumeObject, index) {
+        const usedNames = this.sprite.costumes.map(costume => costume.name);
+        costumeObject.name = StringUtil.unusedName(costumeObject.name, usedNames);
+        this.sprite.costumes.splice(index, 0, costumeObject);
+    }
+
     /**
      * Rename a costume, taking care to avoid duplicate names.
      * @param {int} costumeIndex - the index of the costume to be renamed.
@@ -458,6 +469,17 @@ class RenderedTarget extends Target {
         this.runtime.requestTargetsUpdate(this);
     }
 
+    /**
+     * Add a sound, taking care to avoid duplicate names.
+     * @param {!object} soundObject Object representing the sound.
+     * @param {!int} index Index at which to add costume
+     */
+    addSoundAt (soundObject, index) {
+        const usedNames = this.sprite.sounds.map(sound => sound.name);
+        soundObject.name = StringUtil.unusedName(soundObject.name, usedNames);
+        this.sprite.sounds.splice(index, 0, soundObject);
+    }
+
     /**
      * Add a sound, taking care to avoid duplicate names.
      * @param {!object} soundObject Object representing the sound.
diff --git a/src/virtual-machine.js b/src/virtual-machine.js
index d930ad534..6fdb1d0ec 100644
--- a/src/virtual-machine.js
+++ b/src/virtual-machine.js
@@ -322,11 +322,39 @@ class VirtualMachine extends EventEmitter {
         return loadCostume(md5ext, costumeObject, this.runtime).then(() => {
             this.editingTarget.addCostume(costumeObject);
             this.editingTarget.setCostume(
-                this.editingTarget.sprite.costumes.length - 1
+                this.editingTarget.getCostumes().length - 1
             );
         });
     }
 
+    /**
+     * Duplicate the costume at the given index. Add it at that index + 1.
+     * @param {!int} costumeIndex Index of costume to duplicate
+     */
+    duplicateCostume (costumeIndex) {
+        const originalCostume = this.editingTarget.getCostumes()[costumeIndex];
+        const clone = Object.assign({}, originalCostume);
+        const md5ext = `${clone.assetId}.${clone.dataFormat}`;
+        loadCostume(md5ext, clone, this.runtime).then(() => {
+            this.editingTarget.addCostumeAt(clone, costumeIndex + 1);
+            this.editingTarget.setCostume(costumeIndex + 1);
+            this.emitTargetsUpdate();
+        });
+    }
+
+    /**
+     * Duplicate the sound at the given index. Add it at that index + 1.
+     * @param {!int} soundIndex Index of sound to duplicate
+     */
+    duplicateSound (soundIndex) {
+        const originalSound = this.editingTarget.getSounds()[soundIndex];
+        const clone = Object.assign({}, originalSound);
+        loadSound(clone, this.runtime).then(() => {
+            this.editingTarget.addSoundAt(clone, soundIndex + 1);
+            this.emitTargetsUpdate();
+        });
+    }
+
     /**
      * Rename a costume on the current editing target.
      * @param {int} costumeIndex - the index of the costume to be renamed.