diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 2ad31b6544b..79c14ff35e9 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -139,11 +139,14 @@ declare module 'vscode' {
 		/**
 		 * Start debugging by using either a named launch or named compound configuration,
 		 * or by directly passing a DebugConfiguration.
-		 * Before debugging starts, all unsaved files are saved and the launch configurations are up-to-date.
+		 * The named configurations are looked up in '.vscode/launch.json' found in the given folder.
+		 * Before debugging starts, all unsaved files are saved and the launch configurations are brought up-to-date.
+		 * Folder specific variables used in the configuration (e.g. 'workspaceRoot') are resolved against the given folder.
+		 * @param folder The workspace folder for looking up named configurations and resolving variables or undefined.
 		 * @param nameOrConfiguration Either the name of a debug or compound configuration or a DebugConfiguration object.
 		 * @return A thenable that resolves when debugging could be successfully started.
 		 */
-		export function startDebugging(nameOrConfiguration: string | DebugConfiguration): Thenable<boolean>;
+		export function startDebugging(folder: WorkspaceFolder | undefined, nameOrConfiguration: string | DebugConfiguration): Thenable<boolean>;
 	}
 
 	/**
diff --git a/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts b/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts
index 3956650a100..26fb0e58715 100644
--- a/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts
+++ b/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts
@@ -4,6 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 'use strict';
 
+import URI from 'vs/base/common/uri';
 import { IDisposable, dispose } from 'vs/base/common/lifecycle';
 import { IDebugService, IConfig } from 'vs/workbench/parts/debug/common/debug';
 import { IThreadService } from 'vs/workbench/services/thread/common/threadService';
@@ -44,7 +45,7 @@ export class MainThreadDebugService extends MainThreadDebugServiceShape {
 		this._toDispose = dispose(this._toDispose);
 	}
 
-	public $startDebugging(nameOrConfiguration: string | IConfig): TPromise<boolean> {
+	public $startDebugging(folder: URI | undefined, nameOrConfiguration: string | IConfig): TPromise<boolean> {
 		return this.debugService.startDebugging(nameOrConfiguration).then(x => {
 			return true;
 		}, err => {
diff --git a/src/vs/workbench/api/node/extHost.api.impl.ts b/src/vs/workbench/api/node/extHost.api.impl.ts
index e6bfe3741ac..2a0a102ad37 100644
--- a/src/vs/workbench/api/node/extHost.api.impl.ts
+++ b/src/vs/workbench/api/node/extHost.api.impl.ts
@@ -472,8 +472,8 @@ export function createApiFactory(
 			get activeDebugSession() {
 				return extHostDebugService.activeDebugSession;
 			},
-			startDebugging: proposedApiFunction(extension, (nameOrConfig: string | vscode.DebugConfiguration) => {
-				return extHostDebugService.startDebugging(nameOrConfig);
+			startDebugging: proposedApiFunction(extension, (folder: vscode.WorkspaceFolder | undefined, nameOrConfig: string | vscode.DebugConfiguration) => {
+				return extHostDebugService.startDebugging(folder, nameOrConfig);
 			}),
 			startDebugSession(config: vscode.DebugConfiguration) {
 				return extHostDebugService.startDebugSession(config);
diff --git a/src/vs/workbench/api/node/extHost.protocol.ts b/src/vs/workbench/api/node/extHost.protocol.ts
index d0a34021bf9..ec8445406fc 100644
--- a/src/vs/workbench/api/node/extHost.protocol.ts
+++ b/src/vs/workbench/api/node/extHost.protocol.ts
@@ -347,7 +347,7 @@ export abstract class MainThreadSCMShape {
 export type DebugSessionUUID = string;
 
 export abstract class MainThreadDebugServiceShape {
-	$startDebugging(nameOrConfig: string | vscode.DebugConfiguration): TPromise<boolean> { throw ni(); }
+	$startDebugging(folder: URI | undefined, nameOrConfig: string | vscode.DebugConfiguration): TPromise<boolean> { throw ni(); }
 	$startDebugSession(config: vscode.DebugConfiguration): TPromise<DebugSessionUUID> { throw ni(); }
 	$customDebugAdapterRequest(id: DebugSessionUUID, command: string, args: any): TPromise<any> { throw ni(); }
 }
diff --git a/src/vs/workbench/api/node/extHostDebugService.ts b/src/vs/workbench/api/node/extHostDebugService.ts
index b9dc8d8b7e3..bfb120cd91e 100644
--- a/src/vs/workbench/api/node/extHostDebugService.ts
+++ b/src/vs/workbench/api/node/extHostDebugService.ts
@@ -11,6 +11,7 @@ import { IThreadService } from 'vs/workbench/services/thread/common/threadServic
 import { MainContext, MainThreadDebugServiceShape, ExtHostDebugServiceShape, DebugSessionUUID } from 'vs/workbench/api/node/extHost.protocol';
 
 import * as vscode from 'vscode';
+import URI from 'vs/base/common/uri';
 
 
 export class ExtHostDebugService extends ExtHostDebugServiceShape {
@@ -45,9 +46,9 @@ export class ExtHostDebugService extends ExtHostDebugServiceShape {
 		this._debugServiceProxy = threadService.get(MainContext.MainThreadDebugService);
 	}
 
-	public startDebugging(nameOrConfig: string | vscode.DebugConfiguration): TPromise<boolean> {
+	public startDebugging(folder: vscode.WorkspaceFolder | undefined, nameOrConfig: string | vscode.DebugConfiguration): TPromise<boolean> {
 
-		return this._debugServiceProxy.$startDebugging(nameOrConfig);
+		return this._debugServiceProxy.$startDebugging(folder ? <URI>folder.uri : undefined, nameOrConfig);
 	}
 
 	public startDebugSession(config: vscode.DebugConfiguration): TPromise<vscode.DebugSession> {