diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 6b3227a6cff087d1f1468b908811f8903649b40a..8430b05ab96ef088546259f21367a111a42e4b24 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -189,4 +189,22 @@ declare module 'vscode' {
 		 */
 		onData(callback: (data: string) => any): void;
 	}
+
+	export namespace debug {
+
+		/**
+		 * The currently active debug session or `undefined`. The active debug session is the one
+		 * represented by the debug action floating window or the one currently shown in the drop down menu of the debug action floating window.
+		 * If no debug session is active, the value is `undefined`.
+		 */
+		export const activeDebugSession: DebugSession | undefined;
+
+		/**
+		 * An [event](#Event) which fires when the [active debug session](#debug.activeDebugSession)
+		 * has changed. *Note* that the event also fires when the active debug session changes
+		 * to `undefined`.
+		 */
+		export const onDidChangeActiveDebugSession: Event<DebugSession | undefined>;
+	}
+
 }
diff --git a/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts b/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts
index dc3186f738d2f8876f7811056f5009a7b418b97e..a467704954235c2db764edcadb733f2c7de4b483 100644
--- a/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts
+++ b/src/vs/workbench/api/electron-browser/mainThreadDebugService.ts
@@ -20,9 +20,17 @@ export class MainThreadDebugService extends MainThreadDebugServiceShape {
 		@IDebugService private debugService: IDebugService
 	) {
 		super();
+
 		this._proxy = threadService.get(ExtHostContext.ExtHostDebugService);
 		this._toDispose = [];
 		this._toDispose.push(debugService.onDidEndProcess(proc => this._proxy.$acceptDebugSessionTerminated(<DebugSessionUUID>proc.getId(), proc.configuration.type, proc.name)));
+		this._toDispose.push(debugService.getViewModel().onDidFocusProcess(proc => {
+			if (proc) {
+				this._proxy.$acceptDebugSessionActiveChanged(<DebugSessionUUID>proc.getId(), proc.configuration.type, proc.name);
+			} else {
+				this._proxy.$acceptDebugSessionActiveChanged(undefined);
+			}
+		}));
 	}
 
 	public dispose(): void {
diff --git a/src/vs/workbench/api/node/extHost.api.impl.ts b/src/vs/workbench/api/node/extHost.api.impl.ts
index 56c79673a9b5fdd6fffc5de0b5def7447415d649..2155bc87c32304da01214874403f4728d25b9de7 100644
--- a/src/vs/workbench/api/node/extHost.api.impl.ts
+++ b/src/vs/workbench/api/node/extHost.api.impl.ts
@@ -463,12 +463,19 @@ export function createApiFactory(
 
 		// namespace: debug
 		const debug: typeof vscode.debug = {
+			get activeDebugSession() {
+				assertProposedApi(extension);
+				return extHostDebugService.activeDebugSession;
+			},
 			createDebugSession(config: vscode.DebugConfiguration) {
 				return extHostDebugService.createDebugSession(config);
 			},
 			onDidTerminateDebugSession(listener, thisArg?, disposables?) {
 				return extHostDebugService.onDidTerminateDebugSession(listener, thisArg, disposables);
-			}
+			},
+			onDidChangeActiveDebugSession: proposedApiFunction(extension, (listener, thisArg?, disposables?) => {
+				return extHostDebugService.onDidChangeActiveDebugSession(listener, thisArg, disposables);
+			})
 		};
 
 
diff --git a/src/vs/workbench/api/node/extHost.protocol.ts b/src/vs/workbench/api/node/extHost.protocol.ts
index 31a81ca180995cb16199fb1b334202e042302b50..99db9aa1563151f3659c6c190b00a7028999d1b7 100644
--- a/src/vs/workbench/api/node/extHost.protocol.ts
+++ b/src/vs/workbench/api/node/extHost.protocol.ts
@@ -501,6 +501,7 @@ export abstract class ExtHostTaskShape {
 
 export abstract class ExtHostDebugServiceShape {
 	$acceptDebugSessionTerminated(id: DebugSessionUUID, type: string, name: string): void { throw ni(); }
+	$acceptDebugSessionActiveChanged(id: DebugSessionUUID | undefined, type?: string, name?: string): void { throw ni(); }
 }
 
 // --- proxy identifiers
diff --git a/src/vs/workbench/api/node/extHostDebugService.ts b/src/vs/workbench/api/node/extHostDebugService.ts
index 3b1a496cd6fafcfcc5d90b563288d301381cb4a0..5a16373fe232d9261d5d3f92305728e2cd7cf128 100644
--- a/src/vs/workbench/api/node/extHostDebugService.ts
+++ b/src/vs/workbench/api/node/extHostDebugService.ts
@@ -21,11 +21,18 @@ export class ExtHostDebugService extends ExtHostDebugServiceShape {
 	private _onDidTerminateDebugSession: Emitter<vscode.DebugSession>;
 	get onDidTerminateDebugSession(): Event<vscode.DebugSession> { return this._onDidTerminateDebugSession.event; }
 
+	private _onDidChangeActiveDebugSession: Emitter<vscode.DebugSession | undefined>;
+	get onDidChangeActiveDebugSession(): Event<vscode.DebugSession | undefined> { return this._onDidChangeActiveDebugSession.event; }
+
+	private _activeDebugSession: vscode.DebugSession | undefined;
+	get activeDebugSession(): vscode.DebugSession | undefined { return this._activeDebugSession; }
 
 	constructor(threadService: IThreadService) {
 		super();
 
 		this._onDidTerminateDebugSession = new Emitter<vscode.DebugSession>();
+		this._onDidChangeActiveDebugSession = new Emitter<vscode.DebugSession>();
+
 		this._debugServiceProxy = threadService.get(MainContext.MainThreadDebugService);
 	}
 
@@ -47,6 +54,19 @@ export class ExtHostDebugService extends ExtHostDebugServiceShape {
 		this._onDidTerminateDebugSession.fire(debugSession);
 		this._debugSessions.delete(id);
 	}
+
+	public $acceptDebugSessionActiveChanged(id: DebugSessionUUID | undefined, type?: string, name?: string): void {
+
+		if (id) {
+			this._activeDebugSession = this._debugSessions.get(id);
+			if (!this._activeDebugSession) {
+				this._activeDebugSession = new ExtHostDebugSession(this._debugServiceProxy, id, type, name);
+			}
+		} else {
+			this._activeDebugSession = undefined;
+		}
+		this._onDidChangeActiveDebugSession.fire(this._activeDebugSession);
+	}
 }
 
 export class ExtHostDebugSession implements vscode.DebugSession {
diff --git a/src/vs/workbench/parts/debug/common/debug.ts b/src/vs/workbench/parts/debug/common/debug.ts
index ebba65013cb3a91ba013baca8d01075fba7f281d..182aa4a25fcb9777e29d7f94618a9fdb0986f844 100644
--- a/src/vs/workbench/parts/debug/common/debug.ts
+++ b/src/vs/workbench/parts/debug/common/debug.ts
@@ -273,6 +273,7 @@ export interface IViewModel extends ITreeElement {
 
 	isMultiProcessView(): boolean;
 
+	onDidFocusProcess: Event<IProcess | undefined>;
 	onDidFocusStackFrame: Event<IStackFrame>;
 	onDidSelectExpression: Event<IExpression>;
 	onDidSelectFunctionBreakpoint: Event<IFunctionBreakpoint>;
diff --git a/src/vs/workbench/parts/debug/common/debugViewModel.ts b/src/vs/workbench/parts/debug/common/debugViewModel.ts
index 1db0ec4beadc02d0a01ee790b8bef06de98a4a8c..fa0a2ac2afaa1016323d35d1702ebd51b4043fb6 100644
--- a/src/vs/workbench/parts/debug/common/debugViewModel.ts
+++ b/src/vs/workbench/parts/debug/common/debugViewModel.ts
@@ -12,6 +12,7 @@ export class ViewModel implements debug.IViewModel {
 	private _focusedProcess: debug.IProcess;
 	private selectedExpression: debug.IExpression;
 	private selectedFunctionBreakpoint: debug.IFunctionBreakpoint;
+	private _onDidFocusProcess: Emitter<debug.IProcess | undefined>;
 	private _onDidFocusStackFrame: Emitter<debug.IStackFrame>;
 	private _onDidSelectExpression: Emitter<debug.IExpression>;
 	private _onDidSelectFunctionBreakpoint: Emitter<debug.IFunctionBreakpoint>;
@@ -20,6 +21,7 @@ export class ViewModel implements debug.IViewModel {
 	public changedWorkbenchViewState: boolean;
 
 	constructor(private _selectedConfigurationName: string) {
+		this._onDidFocusProcess = new Emitter<debug.IProcess | undefined>();
 		this._onDidFocusStackFrame = new Emitter<debug.IStackFrame>();
 		this._onDidSelectExpression = new Emitter<debug.IExpression>();
 		this._onDidSelectFunctionBreakpoint = new Emitter<debug.IFunctionBreakpoint>();
@@ -46,10 +48,17 @@ export class ViewModel implements debug.IViewModel {
 
 	public setFocusedStackFrame(stackFrame: debug.IStackFrame, process: debug.IProcess): void {
 		this._focusedStackFrame = stackFrame;
-		this._focusedProcess = process;
+		if (process !== this._focusedProcess) {
+			this._focusedProcess = process;
+			this._onDidFocusProcess.fire(process);
+		}
 		this._onDidFocusStackFrame.fire(stackFrame);
 	}
 
+	public get onDidFocusProcess(): Event<debug.IProcess> {
+		return this._onDidFocusProcess.event;
+	}
+
 	public get onDidFocusStackFrame(): Event<debug.IStackFrame> {
 		return this._onDidFocusStackFrame.event;
 	}