diff --git a/build/tasks/promises_aplus_tests.js b/build/tasks/promises_aplus_tests.js
index 3e770a079..c4fb86d4c 100644
--- a/build/tasks/promises_aplus_tests.js
+++ b/build/tasks/promises_aplus_tests.js
@@ -4,10 +4,20 @@ module.exports = function( grunt ) {
 
 	var spawnTest = require( "./lib/spawn_test.js" );
 
-	grunt.registerTask( "promises_aplus_tests", function() {
+	grunt.registerTask( "promises_aplus_tests",
+		[ "promises_aplus_tests_deferred", "promises_aplus_tests_when" ] );
+
+	grunt.registerTask( "promises_aplus_tests_deferred", function() {
 		spawnTest( this.async(),
 			"./node_modules/.bin/promises-aplus-tests",
-			"test/promises_aplus_adapter.js"
+			"test/promises_aplus_adapter_deferred.js"
+		);
+	} );
+
+	grunt.registerTask( "promises_aplus_tests_when", function() {
+		spawnTest( this.async(),
+			"./node_modules/.bin/promises-aplus-tests",
+			"test/promises_aplus_adapter_when.js"
 		);
 	} );
 };
diff --git a/src/deferred.js b/src/deferred.js
index 0ea1e7f1f..6e4d43b31 100644
--- a/src/deferred.js
+++ b/src/deferred.js
@@ -13,6 +13,38 @@ function Thrower( ex ) {
 	throw ex;
 }
 
+function adoptValue( value, resolve, reject ) {
+	var method;
+
+	try {
+
+		// Check for promise aspect first to privilege synchronous behavior
+		if ( value && jQuery.isFunction( ( method = value.promise ) ) ) {
+			method.call( value ).done( resolve ).fail( reject );
+
+		// Other thenables
+		} else if ( value && jQuery.isFunction( ( method = value.then ) ) ) {
+			method.call( value, resolve, reject );
+
+		// Other non-thenables
+		} else {
+
+			// Support: Android 4.0 only
+			// Strict mode functions invoked without .call/.apply get global-object context
+			resolve.call( undefined, value );
+		}
+
+	// For Promises/A+, convert exceptions into rejections
+	// Since jQuery.when doesn't unwrap thenables, we can skip the extra checks appearing in
+	// Deferred#then to conditionally suppress rejection.
+	} catch ( /*jshint -W002 */ value ) {
+
+		// Support: Android 4.0 only
+		// Strict mode functions invoked without .call/.apply get global-object context
+		reject.call( undefined, value );
+	}
+}
+
 jQuery.extend( {
 
 	Deferred: function( func ) {
@@ -305,67 +337,45 @@ jQuery.extend( {
 	},
 
 	// Deferred helper
-	when: function() {
-		var method, resolveContexts,
-			i = 0,
+	when: function( singleValue ) {
+		var
+
+			// count of uncompleted subordinates
+			remaining = arguments.length,
+
+			// count of unprocessed arguments
+			i = remaining,
+
+			// subordinate fulfillment data
+			resolveContexts = Array( i ),
 			resolveValues = slice.call( arguments ),
-			length = resolveValues.length,
 
-			// the count of uncompleted subordinates
-			remaining = length,
-
-			// the master Deferred.
+			// the master Deferred
 			master = jQuery.Deferred(),
 
-			// Update function for both resolving subordinates
+			// subordinate callback factory
 			updateFunc = function( i ) {
 				return function( value ) {
 					resolveContexts[ i ] = this;
 					resolveValues[ i ] = arguments.length > 1 ? slice.call( arguments ) : value;
 					if ( !( --remaining ) ) {
-						master.resolveWith(
-							resolveContexts.length === 1 ? resolveContexts[ 0 ] : resolveContexts,
-							resolveValues
-						);
+						master.resolveWith( resolveContexts, resolveValues );
 					}
 				};
 			};
 
-		// Add listeners to promise-like subordinates; treat others as resolved
-		if ( length > 0 ) {
-			resolveContexts = new Array( length );
-			for ( ; i < length; i++ ) {
+		// Single- and empty arguments are adopted like Promise.resolve
+		if ( remaining <= 1 ) {
+			adoptValue( singleValue, master.resolve, master.reject );
 
-				// jQuery.Deferred - treated specially to get resolve-sync behavior
-				if ( resolveValues[ i ] &&
-					jQuery.isFunction( ( method = resolveValues[ i ].promise ) ) ) {
-
-					method.call( resolveValues[ i ] )
-						.done( updateFunc( i ) )
-						.fail( master.reject );
-
-				// Other thenables
-				} else if ( resolveValues[ i ] &&
-					jQuery.isFunction( ( method = resolveValues[ i ].then ) ) ) {
-
-					method.call(
-						resolveValues[ i ],
-						updateFunc( i ),
-						master.reject
-					);
-				} else {
-
-					// Support: Android 4.0 only
-					// Strict mode functions invoked without .call/.apply get global-object context
-					updateFunc( i ).call( undefined, resolveValues[ i ] );
-				}
-			}
-
-		// If we're not waiting on anything, resolve the master
-		} else {
-			master.resolveWith();
+			// Use .then() to unwrap secondary thenables (cf. gh-3000)
+			return master.then();
 		}
 
+		// Multiple arguments are aggregated like Promise.all array elements
+		while ( i-- ) {
+			adoptValue( resolveValues[ i ], updateFunc( i ), master.reject );
+		}
 		return master.promise();
 	}
 } );
diff --git a/test/promises_aplus_adapter.js b/test/promises_aplus_adapter_deferred.js
similarity index 100%
rename from test/promises_aplus_adapter.js
rename to test/promises_aplus_adapter_deferred.js
diff --git a/test/promises_aplus_adapter_when.js b/test/promises_aplus_adapter_when.js
new file mode 100644
index 000000000..0a5ec6756
--- /dev/null
+++ b/test/promises_aplus_adapter_when.js
@@ -0,0 +1,51 @@
+/* jshint node: true */
+
+"use strict";
+
+require( "jsdom" ).env( "", function( errors, window ) {
+	if ( errors ) {
+		console.error( errors );
+		return;
+	}
+
+	var jQuery = require( ".." )( window );
+
+	exports.deferred = function() {
+		var adopted, promised,
+			obj = {
+				resolve: function() {
+					if ( !adopted ) {
+						adopted = jQuery.when.apply( jQuery, arguments );
+						if ( promised ) {
+							adopted.then( promised.resolve, promised.reject );
+						}
+					}
+					return adopted;
+				},
+				reject: function( value ) {
+					if ( !adopted ) {
+						adopted = jQuery.when( jQuery.Deferred().reject( value ) );
+						if ( promised ) {
+							adopted.then( promised.resolve, promised.reject );
+						}
+					}
+					return adopted;
+				},
+
+				// A manually-constructed thenable that works even if calls precede resolve/reject
+				promise: {
+					then: function() {
+						if ( !adopted ) {
+							if ( !promised ) {
+								promised = jQuery.Deferred();
+							}
+							return promised.then.apply( promised, arguments );
+						}
+						return adopted.then.apply( adopted, arguments );
+					}
+				}
+			};
+
+		return obj;
+	};
+} );
diff --git a/test/unit/deferred.js b/test/unit/deferred.js
index 305740fa4..830103eeb 100644
--- a/test/unit/deferred.js
+++ b/test/unit/deferred.js
@@ -761,11 +761,30 @@ QUnit.test( "jQuery.Deferred - notify and resolve", function( assert ) {
 	} );
 } );
 
-QUnit.test( "jQuery.when", function( assert ) {
 
-	assert.expect( 37 );
+QUnit.test( "jQuery.when(nonThenable) - like Promise.resolve", function( assert ) {
+	"use strict";
+
+	assert.expect( 44 );
+
+	var
+
+		// Support: Android 4.0 only
+		// Strict mode functions invoked without .call/.apply get global-object context
+		defaultContext = (function getDefaultContext() { return this; }).call(),
+
+		done = assert.async( 20 );
+
+	jQuery.when()
+		.done( function( resolveValue ) {
+			assert.strictEqual( resolveValue, undefined, "Resolved .done with no arguments" );
+			assert.strictEqual( this, defaultContext, "Default .done context with no arguments" );
+		} )
+		.then( function( resolveValue ) {
+			assert.strictEqual( resolveValue, undefined, "Resolved .then with no arguments" );
+			assert.strictEqual( this, defaultContext, "Default .then context with no arguments" );
+		} );
 
-	// Some other objects
 	jQuery.each( {
 		"an empty string": "",
 		"a non-empty string": "some string",
@@ -778,51 +797,136 @@ QUnit.test( "jQuery.when", function( assert ) {
 		"a plain object": {},
 		"an array": [ 1, 2, 3 ]
 	}, function( message, value ) {
-		assert.ok(
-			jQuery.isFunction(
-				jQuery.when( value ).done( function( resolveValue ) {
-					assert.strictEqual( this, window, "Context is the global object with " + message );
-					assert.strictEqual( resolveValue, value, "Test the promise was resolved with " + message );
-				} ).promise
-			),
-			"Test " + message + " triggers the creation of a new Promise"
-		);
-	} );
-
-	assert.ok(
-		jQuery.isFunction(
-			jQuery.when().done( function( resolveValue ) {
-				assert.strictEqual( this, window, "Test the promise was resolved with window as its context" );
-				assert.strictEqual( resolveValue, undefined, "Test the promise was resolved with no parameter" );
-			} ).promise
-		),
-		"Test calling when with no parameter triggers the creation of a new Promise"
-	);
-
-	var cache,
-		context = {};
-
-	jQuery.when( jQuery.Deferred().resolveWith( context ) ).done( function() {
-		assert.strictEqual( this, context, "when( promise ) propagates context" );
-	} );
-
-	jQuery.each( [ 1, 2, 3 ], function( k, i ) {
-		jQuery.when( cache || jQuery.Deferred( function() {
-				this.resolve( i );
-			} )
-		).done( function( value ) {
-			assert.strictEqual( value, 1, "Function executed" + ( i > 1 ? " only once" : "" ) );
-			cache = value;
-		} );
+		var code = "jQuery.when( " + message + " )",
+			onFulfilled = function( method ) {
+				var call = code + "." + method;
+				return function( resolveValue ) {
+					assert.strictEqual( resolveValue, value, call + " resolve" );
+					assert.strictEqual( this, defaultContext, call + " context" );
+					done();
+				};
+			},
+			onRejected = function( method ) {
+				var call = code + "." + method;
+				return function() {
+					assert.ok( false, call + " reject" );
+					done();
+				};
+			};
 
+		jQuery.when( value )
+			.done( onFulfilled( "done" ) )
+			.fail( onRejected( "done" ) )
+			.then( onFulfilled( "then" ), onRejected( "then" ) );
 	} );
 } );
 
-QUnit.test( "jQuery.when - joined", function( assert ) {
+QUnit.test( "jQuery.when(thenable) - like Promise.resolve", function( assert ) {
+	"use strict";
 
-	assert.expect( 81 );
+	assert.expect( 56 );
 
-	var deferreds = {
+	var slice = [].slice,
+		sentinel = { context: "explicit" },
+		eventuallyFulfilled = jQuery.Deferred().notify( true ),
+		eventuallyRejected = jQuery.Deferred().notify( true ),
+		inputs = {
+			promise: Promise.resolve( true ),
+			rejectedPromise: Promise.reject( false ),
+			deferred: jQuery.Deferred().resolve( true ),
+			eventuallyFulfilled: eventuallyFulfilled,
+			secondaryFulfilled: jQuery.Deferred().resolve( eventuallyFulfilled ),
+			multiDeferred: jQuery.Deferred().resolve( "foo", "bar" ),
+			deferredWith: jQuery.Deferred().resolveWith( sentinel, [ true ] ),
+			multiDeferredWith: jQuery.Deferred().resolveWith( sentinel, [ "foo", "bar" ] ),
+			rejectedDeferred: jQuery.Deferred().reject( false ),
+			eventuallyRejected: eventuallyRejected,
+			secondaryRejected: jQuery.Deferred().resolve( eventuallyRejected ),
+			multiRejectedDeferred: jQuery.Deferred().reject( "baz", "quux" ),
+			rejectedDeferredWith: jQuery.Deferred().rejectWith( sentinel, [ false ] ),
+			multiRejectedDeferredWith: jQuery.Deferred().rejectWith( sentinel, [ "baz", "quux" ] )
+		},
+		contexts = {
+			deferredWith: sentinel,
+			multiDeferredWith: sentinel,
+			rejectedDeferredWith: sentinel,
+			multiRejectedDeferredWith: sentinel
+		},
+		willSucceed = {
+			promise: [ true ],
+			deferred: [ true ],
+			eventuallyFulfilled: [ true ],
+			secondaryFulfilled: [ true ],
+			multiDeferred: [ "foo", "bar" ],
+			deferredWith: [ true ],
+			multiDeferredWith: [ "foo", "bar" ]
+		},
+		willError = {
+			rejectedPromise: [ false ],
+			rejectedDeferred: [ false ],
+			eventuallyRejected: [ false ],
+			secondaryRejected: [ false ],
+			multiRejectedDeferred: [ "baz", "quux" ],
+			rejectedDeferredWith: [ false ],
+			multiRejectedDeferredWith: [ "baz", "quux" ]
+		},
+
+		// Support: Android 4.0 only
+		// Strict mode functions invoked without .call/.apply get global-object context
+		defaultContext = (function getDefaultContext() { return this; }).call(),
+
+		done = assert.async( 28 );
+
+	jQuery.each( inputs, function( message, value ) {
+		var code = "jQuery.when( " + message + " )",
+			shouldResolve = willSucceed[ message ],
+			shouldError = willError[ message ],
+			context = contexts[ message ] || defaultContext,
+			onFulfilled = function( method ) {
+				var call = code + "." + method;
+				return function() {
+					if ( shouldResolve ) {
+						assert.deepEqual( slice.call( arguments ), shouldResolve,
+							call + " resolve" );
+						assert.strictEqual( this, context, call + " context" );
+					} else {
+						assert.ok( false,  call + " resolve" );
+					}
+					done();
+				};
+			},
+			onRejected = function( method ) {
+				var call = code + "." + method;
+				return function() {
+					if ( shouldError ) {
+						assert.deepEqual( slice.call( arguments ), shouldError, call + " reject" );
+						assert.strictEqual( this, context, call + " context" );
+					} else {
+						assert.ok( false, call + " reject" );
+					}
+					done();
+				};
+			};
+
+		jQuery.when( value )
+			.done( onFulfilled( "done" ) )
+			.fail( onRejected( "done" ) )
+			.then( onFulfilled( "then" ), onRejected( "then" ) );
+	} );
+
+	setTimeout( function() {
+		eventuallyFulfilled.resolve( true );
+		eventuallyRejected.reject( false );
+	}, 50 );
+} );
+
+QUnit.test( "jQuery.when(a, b) - like Promise.all", function( assert ) {
+	"use strict";
+
+	assert.expect( 196 );
+
+	var slice = [].slice,
+		deferreds = {
 			rawValue: 1,
 			fulfilled: jQuery.Deferred().resolve( 1 ),
 			rejected: jQuery.Deferred().reject( 0 ),
@@ -842,46 +946,91 @@ QUnit.test( "jQuery.when - joined", function( assert ) {
 			eventuallyRejected: true,
 			rejectedStandardPromise: true
 		},
-		counter = 49,
 
 		// Support: Android 4.0 only
 		// Strict mode functions invoked without .call/.apply get global-object context
-		expectedContext = (function() { "use strict"; return this; }).call();
+		defaultContext = (function getDefaultContext() { return this; }).call(),
 
-	QUnit.stop();
+		done = assert.async( 98 );
 
-	function restart() {
-		if ( !--counter ) {
-			QUnit.start();
-		}
-	}
-
-	jQuery.each( deferreds, function( id1, defer1 ) {
-		jQuery.each( deferreds, function( id2, defer2 ) {
-			var shouldResolve = willSucceed[ id1 ] && willSucceed[ id2 ],
+	jQuery.each( deferreds, function( id1, v1 ) {
+		jQuery.each( deferreds, function( id2, v2 ) {
+			var code = "jQuery.when( " + id1 + ", " + id2 + " )",
+				shouldResolve = willSucceed[ id1 ] && willSucceed[ id2 ],
 				shouldError = willError[ id1 ] || willError[ id2 ],
-				expected = shouldResolve ? [ 1, 1 ] : [ 0, undefined ],
-				code = "jQuery.when( " + id1 + ", " + id2 + " )";
+				expected = shouldResolve ? [ 1, 1 ] : [ 0 ],
+				context = shouldResolve ? [ defaultContext, defaultContext ] : defaultContext,
+				onFulfilled = function( method ) {
+					var call = code + "." + method;
+					return function() {
+						if ( shouldResolve ) {
+							assert.deepEqual( slice.call( arguments ), expected,
+								call + " resolve" );
+							assert.deepEqual( this, context, code + " context" );
+						} else {
+							assert.ok( false,  call + " resolve" );
+						}
+						done();
+					};
+				},
+				onRejected = function( method ) {
+					var call = code + "." + method;
+					return function() {
+						if ( shouldError ) {
+							assert.deepEqual( slice.call( arguments ), expected, call + " reject" );
+							assert.deepEqual( this, context, code + " context" );
+						} else {
+							assert.ok( false, call + " reject" );
+						}
+						done();
+					};
+				};
 
-			jQuery.when( defer1, defer2 ).done( function( a, b ) {
-				if ( shouldResolve ) {
-					assert.deepEqual( [ a, b ], expected, code + " => resolve" );
-					assert.strictEqual( this[ 0 ], expectedContext, code + " => context[0] OK" );
-					assert.strictEqual( this[ 1 ], expectedContext, code + " => context[1] OK" );
-				} else {
-					assert.ok( false,  code + " => resolve" );
-				}
-			} ).fail( function( a, b ) {
-				if ( shouldError ) {
-					assert.deepEqual( [ a, b ], expected, code + " => reject" );
-				} else {
-					assert.ok( false, code + " => reject" );
-				}
-			} ).always( restart );
+			jQuery.when( v1, v2 )
+				.done( onFulfilled( "done" ) )
+				.fail( onRejected( "done" ) )
+				.then( onFulfilled( "then" ), onRejected( "then" ) );
+		} );
+	} );
+
+	setTimeout( function() {
+		deferreds.eventuallyFulfilled.resolve( 1 );
+		deferreds.eventuallyRejected.reject( 0 );
+	}, 50 );
+} );
+
+QUnit.test( "jQuery.when - always returns a new promise", function( assert ) {
+
+	assert.expect( 42 );
+
+	jQuery.each( {
+		"no arguments": [],
+		"non-thenable": [ "foo" ],
+		"promise": [ Promise.resolve( "bar" ) ],
+		"rejected promise": [ Promise.reject( "bar" ) ],
+		"deferred": [ jQuery.Deferred().resolve( "baz" ) ],
+		"rejected deferred": [ jQuery.Deferred().reject( "baz" ) ],
+		"multi-resolved deferred": [ jQuery.Deferred().resolve( "qux", "quux" ) ],
+		"multiple non-thenables": [ "corge", "grault" ],
+		"multiple deferreds": [
+			jQuery.Deferred().resolve( "garply" ),
+			jQuery.Deferred().resolve( "waldo" )
+		]
+	}, function( label, args ) {
+		var result = jQuery.when.apply( jQuery, args );
+
+		assert.ok( jQuery.isFunction( result.then ), "Thenable returned from " + label );
+		assert.strictEqual( result.resolve, undefined, "Non-deferred returned from " + label );
+		assert.strictEqual( result.promise(), result, "Promise returned from " + label );
+
+		jQuery.each( args, function( i, arg ) {
+			assert.notStrictEqual( result, arg, "Returns distinct from arg " + i + " of " + label );
+			if ( arg.promise ) {
+				assert.notStrictEqual( result, arg.promise(),
+					"Returns distinct from promise of arg " + i + " of " + label );
+			}
 		} );
 	} );
-	deferreds.eventuallyFulfilled.resolve( 1 );
-	deferreds.eventuallyRejected.reject( 0 );
 } );
 
 QUnit.test( "jQuery.when - notify does not affect resolved", function( assert ) {
@@ -900,107 +1049,3 @@ QUnit.test( "jQuery.when - notify does not affect resolved", function( assert )
 		assert.ok( false, "Error on resolve" );
 	} );
 } );
-
-QUnit.test( "jQuery.when - filtering", function( assert ) {
-
-	assert.expect( 2 );
-
-	function increment( x ) {
-		return x + 1;
-	}
-
-	QUnit.stop();
-
-	jQuery.when(
-		jQuery.Deferred().resolve( 3 ).then( increment ),
-		jQuery.Deferred().reject( 5 ).then( null, increment )
-	).done( function( four, six ) {
-		assert.strictEqual( four, 4, "resolved value incremented" );
-		assert.strictEqual( six, 6, "rejected value incremented" );
-		QUnit.start();
-	} );
-} );
-
-QUnit.test( "jQuery.when - exceptions", function( assert ) {
-
-	assert.expect( 2 );
-
-	function woops() {
-		throw "exception thrown";
-	}
-
-	QUnit.stop();
-
-	jQuery.Deferred().resolve().then( woops ).fail( function( doneException ) {
-		assert.strictEqual( doneException, "exception thrown", "throwing in done handler" );
-		jQuery.Deferred().reject().then( null, woops ).fail( function( failException ) {
-			assert.strictEqual( failException, "exception thrown", "throwing in fail handler" );
-			QUnit.start();
-		} );
-	} );
-} );
-
-QUnit.test( "jQuery.when - chaining", function( assert ) {
-
-	assert.expect( 4 );
-
-	var defer = jQuery.Deferred();
-
-	function chain() {
-		return defer;
-	}
-
-	function chainStandard() {
-		return Promise.resolve( "std deferred" );
-	}
-
-	QUnit.stop();
-
-	jQuery.when(
-		jQuery.Deferred().resolve( 3 ).then( chain ),
-		jQuery.Deferred().reject( 5 ).then( null, chain ),
-		jQuery.Deferred().resolve( 3 ).then( chainStandard ),
-		jQuery.Deferred().reject( 5 ).then( null, chainStandard )
-	).done( function( v1, v2, s1, s2 ) {
-		assert.strictEqual( v1, "other deferred", "chaining in done handler" );
-		assert.strictEqual( v2, "other deferred", "chaining in fail handler" );
-		assert.strictEqual( s1, "std deferred", "chaining thenable in done handler" );
-		assert.strictEqual( s2, "std deferred", "chaining thenable in fail handler" );
-		QUnit.start();
-	} );
-
-	defer.resolve( "other deferred" );
-} );
-
-QUnit.test( "jQuery.when - solitary thenables", function( assert ) {
-
-	assert.expect( 1 );
-
-	var done = assert.async(),
-		rejected = new Promise( function( resolve, reject ) {
-			setTimeout( function() {
-				reject( "rejected" );
-			}, 100 );
-		} );
-
-	jQuery.when( rejected ).then(
-		function() {
-			assert.ok( false, "Rejected, solitary, non-Deferred thenable should not resolve" );
-			done();
-		},
-		function() {
-			assert.ok( true, "Rejected, solitary, non-Deferred thenable rejected properly" );
-			done();
-		}
-	);
-} );
-
-QUnit.test( "jQuery.when does not reuse a solitary jQuery Deferred (gh-2018)", function( assert ) {
-
-	assert.expect( 2 );
-	var defer = jQuery.Deferred().resolve(),
-		promise = jQuery.when( defer );
-
-	assert.equal( promise.state(), "resolved", "Master Deferred is immediately resolved" );
-	assert.notStrictEqual( defer.promise(), promise, "jQuery.when returns the master deferred's promise" );
-} );
diff --git a/test/unit/effects.js b/test/unit/effects.js
index 5f1913575..2b953cd35 100644
--- a/test/unit/effects.js
+++ b/test/unit/effects.js
@@ -1028,7 +1028,7 @@ jQuery.each( {
 				jQuery( elem ).remove();
 
 			} );
-			this.clock.tick( 50 );
+			this.clock.tick( 100 );
 		} );
 	} );
 } );