diff --git a/src/vs/workbench/api/node/extHostExtensionActivator.ts b/src/vs/workbench/api/node/extHostExtensionActivator.ts
index c37e7b2dfe7..5a2f21ebdee 100644
--- a/src/vs/workbench/api/node/extHostExtensionActivator.ts
+++ b/src/vs/workbench/api/node/extHostExtensionActivator.ts
@@ -237,35 +237,39 @@ export class ExtensionsActivator {
 	 * semantics: `redExtensions` must wait for `greenExtensions`.
 	 */
 	private _handleActivateRequest(currentExtension: IExtensionDescription, greenExtensions: { [id: string]: IExtensionDescription; }, redExtensions: IExtensionDescription[]): void {
-		let depIds = (typeof currentExtension.extensionDependencies === 'undefined' ? [] : currentExtension.extensionDependencies);
+		let dependencies = (typeof currentExtension.extensionDependencies === 'undefined' ? [] : currentExtension.extensionDependencies);
 		let currentExtensionGetsGreenLight = true;
 
-		for (let j = 0, lenJ = depIds.length; j < lenJ; j++) {
-			let depId = depIds[j];
-			let depDesc = this._registry.getExtensionDescription(depId);
+		for (let j = 0, lenJ = dependencies.length; j < lenJ; j++) {
+			const dependency = dependencies[j];
+			const depId: string = typeof dependency === 'string' ? dependency : dependency.optional ? null : dependency.id;
 
-			if (!depDesc) {
-				// Error condition 1: unknown dependency
-				this._host.showMessage(Severity.Error, nls.localize('unknownDep', "Extension '{1}' failed to activate. Reason: unknown dependency '{0}'.", depId, currentExtension.id));
-				const error = new Error(`Unknown dependency '${depId}'`);
-				this._activatedExtensions[currentExtension.id] = new FailedExtension(error);
-				return;
-			}
+			if (depId) {
+				let depDesc = this._registry.getExtensionDescription(depId);
 
-			if (hasOwnProperty.call(this._activatedExtensions, depId)) {
-				let dep = this._activatedExtensions[depId];
-				if (dep.activationFailed) {
-					// Error condition 2: a dependency has already failed activation
-					this._host.showMessage(Severity.Error, nls.localize('failedDep1', "Extension '{1}' failed to activate. Reason: dependency '{0}' failed to activate.", depId, currentExtension.id));
-					const error = new Error(`Dependency ${depId} failed to activate`);
-					(<any>error).detail = dep.activationFailedError;
+				if (!depDesc) {
+					// Error condition 1: unknown dependency
+					this._host.showMessage(Severity.Error, nls.localize('unknownDep', "Extension '{1}' failed to activate. Reason: unknown dependency '{0}'.", depId, currentExtension.id));
+					const error = new Error(`Unknown dependency '${depId}'`);
 					this._activatedExtensions[currentExtension.id] = new FailedExtension(error);
 					return;
 				}
-			} else {
-				// must first wait for the dependency to activate
-				currentExtensionGetsGreenLight = false;
-				greenExtensions[depId] = depDesc;
+
+				if (hasOwnProperty.call(this._activatedExtensions, depId)) {
+					let dep = this._activatedExtensions[depId];
+					if (dep.activationFailed) {
+						// Error condition 2: a dependency has already failed activation
+						this._host.showMessage(Severity.Error, nls.localize('failedDep1', "Extension '{1}' failed to activate. Reason: dependency '{0}' failed to activate.", depId, currentExtension.id));
+						const error = new Error(`Dependency ${depId} failed to activate`);
+						(<any>error).detail = dep.activationFailedError;
+						this._activatedExtensions[currentExtension.id] = new FailedExtension(error);
+						return;
+					}
+				} else {
+					// must first wait for the dependency to activate
+					currentExtensionGetsGreenLight = false;
+					greenExtensions[depId] = depDesc;
+				}
 			}
 		}
 
diff --git a/src/vs/workbench/services/extensions/common/extensions.ts b/src/vs/workbench/services/extensions/common/extensions.ts
index d8bfa847f36..24e6771a154 100644
--- a/src/vs/workbench/services/extensions/common/extensions.ts
+++ b/src/vs/workbench/services/extensions/common/extensions.ts
@@ -21,7 +21,7 @@ export interface IExtensionDescription {
 	readonly isBuiltin: boolean;
 	readonly isUnderDevelopment: boolean;
 	readonly extensionLocation: URI;
-	readonly extensionDependencies?: string[];
+	readonly extensionDependencies?: Array<string | { id: string, optional?: boolean }>;
 	readonly activationEvents?: string[];
 	readonly engines: {
 		vscode: string;
diff --git a/src/vs/workbench/services/extensions/node/extensionPoints.ts b/src/vs/workbench/services/extensions/node/extensionPoints.ts
index 90cfe42920d..71de9bb715a 100644
--- a/src/vs/workbench/services/extensions/node/extensionPoints.ts
+++ b/src/vs/workbench/services/extensions/node/extensionPoints.ts
@@ -387,8 +387,8 @@ class ExtensionManifestValidator extends ExtensionManifestHandler {
 			return false;
 		}
 		if (typeof extensionDescription.extensionDependencies !== 'undefined') {
-			if (!ExtensionManifestValidator._isStringArray(extensionDescription.extensionDependencies)) {
-				notices.push(nls.localize('extensionDescription.extensionDependencies', "property `{0}` can be omitted or must be of type `string[]`", 'extensionDependencies'));
+			if (!ExtensionManifestValidator._isExtensionDependencyArray(extensionDescription.extensionDependencies)) {
+				notices.push(nls.localize('extensionDescription.extensionDependencies', "property `{0}` can be omitted or must be an array of type `string` or `{id: string, optional: boolean}`", 'extensionDependencies'));
 				return false;
 			}
 		}
@@ -433,6 +433,26 @@ class ExtensionManifestValidator extends ExtensionManifestHandler {
 		}
 		return true;
 	}
+
+	private static _isExtensionDependencyArray(arr: any[]): boolean {
+		if (!Array.isArray(arr)) {
+			return false;
+		}
+		for (let i = 0, len = arr.length; i < len; i++) {
+			if (typeof arr[i] !== 'string') {
+				if (typeof arr[i] !== 'object') {
+					return false;
+				}
+				if (typeof arr[i]['id'] !== 'string') {
+					return false;
+				}
+				if (typeof arr[i]['optional'] !== 'undefined' && typeof arr[i]['optional'] !== 'boolean') {
+					return false;
+				}
+			}
+		}
+		return true;
+	}
 }
 
 export class ExtensionScannerInput {