diff --git a/main/Command.scala b/main/Command.scala
index 3b5567062..cbeeddab4 100644
--- a/main/Command.scala
+++ b/main/Command.scala
@@ -39,7 +39,7 @@ object Command
 	def apply[T](name: String, briefHelp: (String, String), detail: String)(parser: State => Parser[T])(effect: (State,T) => State): Command =
 		apply(name, Help(name, briefHelp, detail) )(parser)(effect)
 	def apply[T](name: String, help: Help*)(parser: State => Parser[T])(effect: (State,T) => State): Command  =
-		make(name, help : _* )(s => applyEffect(parser(s))(t => effect(s,t)) )
+		make(name, help : _* )(applyEffect(parser)(effect) )
 
 	def args(name: String, briefHelp: (String, String), detail: String, display: String)(f: (State, Seq[String]) => State): Command =
 		args(name, display, Help(name, briefHelp, detail) )(f)
@@ -53,9 +53,12 @@ object Command
 		make(name, help : _*)( state => token(trimmed(any.+.string) map apply1(f, state)) )
 	
 	def custom(parser: State => Parser[() => State], help: Seq[Help] = Nil): Command  =  new ArbitraryCommand(parser, help, AttributeMap.empty)
+	def arb[T](parser: State => Parser[T], help: Help*)(effect: (State, T) => State): Command  =  custom(applyEffect(parser)(effect), help)
 
 	def validID(name: String) = DefaultParsers.matches(OpOrID, name)
 
+	def applyEffect[T](parser: State => Parser[T])(effect: (State, T) => State): State => Parser[() => State] =
+		s => applyEffect(parser(s))(t => effect(s,t))
 	def applyEffect[T](p: Parser[T])(f: T => State): Parser[() => State] =
 		p map { t => () => f(t) }
 
diff --git a/main/Cross.scala b/main/Cross.scala
new file mode 100644
index 000000000..6b8655fd9
--- /dev/null
+++ b/main/Cross.scala
@@ -0,0 +1,50 @@
+/* sbt -- Simple Build Tool
+ * Copyright 2011 Mark Harrah
+ */
+package sbt
+
+	import Keys._
+	import complete.{DefaultParsers, Parser}
+	import DefaultParsers._
+
+
+object Cross
+{
+	final val Switch = "++"
+	final val Cross = "+"
+
+	def switchParser(state: State): Parser[(String, String)] =
+	{
+		val knownVersions = crossVersions(state)
+		token(Switch ~ Space) flatMap { _ => token(NotSpace.examples(knownVersions : _*)) ~ (token(Space ~> matched(state.combinedParser)) ?? "") }
+	}
+	lazy val switchVersion = Command.arb(requireSession(switchParser)) { case (state, (version, command)) =>
+		val x = Project.extract(state)
+			import x._
+		val add = (scalaVersion := version) :: Nil
+		val append = Load.transformSettings(Load.projectScope(currentRef), currentRef.build, rootProject, add)
+		val newStructure = Load.reapply(session.original ++ append, structure)
+		Project.setProject(session, newStructure, command :: state)
+	}
+
+	def crossParser(state: State): Parser[String] =
+		token(Cross ~ Space) flatMap { _ => token(matched(state.combinedParser)) }
+
+	lazy val crossBuild = Command.arb(requireSession(crossParser)) { (state, command) =>
+		val x = Project.extract(state)
+			import x._
+		val versions = crossVersions(state)
+		val current = scalaVersion in currentRef get structure.data map(Switch + " " + _) toList;
+		if(versions.isEmpty) command :: state else versions.map(Switch + " " + _ + " " + command) ::: current ::: state
+	}
+	def crossVersions(state: State): Seq[String] =
+	{
+		val x = Project.extract(state)
+			import x._
+		crossScalaVersions in currentRef get structure.data getOrElse Nil
+	}
+	
+	def requireSession[T](p: State => Parser[T]): State => Parser[T] = s =>
+		if(s get sessionSettings isEmpty) failure("No project loaded") else p(s)
+
+}
\ No newline at end of file
diff --git a/main/Defaults.scala b/main/Defaults.scala
index f446efdf3..17424d84a 100644
--- a/main/Defaults.scala
+++ b/main/Defaults.scala
@@ -125,6 +125,7 @@ object Defaults
 		scalacOptions in GlobalScope :== Nil,
 		scalaInstance <<= scalaInstanceSetting,
 		scalaVersion in GlobalScope <<= appConfiguration( _.provider.scalaProvider.version),
+		crossScalaVersions <<= Seq(scalaVersion).join,
 		target <<= (target, scalaInstance, crossPaths)( (t,si,cross) => if(cross) t / ("scala-" + si.actualVersion) else t )
 	)
 
diff --git a/main/Keys.scala b/main/Keys.scala
index 84858ca03..2d0fe1b3e 100644
--- a/main/Keys.scala
+++ b/main/Keys.scala
@@ -76,6 +76,7 @@ object Keys
 	val scalaHome = SettingKey[Option[File]]("scala-home")
 	val scalaInstance = SettingKey[ScalaInstance]("scala-instance")
 	val scalaVersion = SettingKey[String]("scala-version")
+	val crossScalaVersions = SettingKey[Seq[String]]("cross-scala-versions")
 	val classpathOptions = SettingKey[ClasspathOptions]("classpath-options")
 	val definedSbtPlugins = TaskKey[Set[String]]("defined-sbt-plugins")
 	val sbtPlugin = SettingKey[Boolean]("sbt-plugin")
diff --git a/main/Main.scala b/main/Main.scala
index 36734d621..a1622f402 100644
--- a/main/Main.scala
+++ b/main/Main.scala
@@ -4,10 +4,10 @@
 package sbt
 
 	import Execute.NodeView
-	import complete.HistoryCommands
+	import complete.{DefaultParsers, HistoryCommands, Parser}
 	import HistoryCommands.{Start => HistoryPrefix}
 	import compiler.EvalImports
-	import sbt.complete.{DefaultParsers, Parser}
+
 
 	import Command.applyEffect
 	import Keys.{analysis,historyPath,logged,shellPrompt}
@@ -59,7 +59,7 @@ class xMain extends xsbti.AppMain
 	import CommandSupport._
 object BuiltinCommands
 {
-	def DefaultCommands: Seq[Command] = Seq(ignore, help, reboot, read, history, continuous, exit, loadProject, loadProjectImpl, loadFailed, Script.command,
+	def DefaultCommands: Seq[Command] = Seq(ignore, help, reboot, read, history, continuous, exit, loadProject, loadProjectImpl, loadFailed, Script.command, Cross.crossBuild, Cross.switchVersion,
 		projects, project, setOnFailure, clearOnFailure, ifLast, multi, shell, set, inspect, eval, alias, append, last, lastGrep, nop, sessionCommand, act)
 	def DefaultBootCommands: Seq[String] = LoadProject :: (IfLast + " " + Shell) :: Nil