diff --git a/src/WindowMaker.h b/src/WindowMaker.h
index 3c2869c6..606298d1 100644
--- a/src/WindowMaker.h
+++ b/src/WindowMaker.h
@@ -463,6 +463,7 @@ extern struct WPreferences {
 	char show_clip_title;
 
 	struct {
+		unsigned int replace:1;               /* replace existing window manager */
 		unsigned int nodock:1;                /* don't display the dock */
 		unsigned int noclip:1;                /* don't display the clip */
 		unsigned int clip_merged_in_dock:1;   /* disable clip, switch workspaces with dock */
diff --git a/src/event.c b/src/event.c
index dbb927bd..1e100f77 100644
--- a/src/event.c
+++ b/src/event.c
@@ -103,6 +103,7 @@ static void handleFocusIn(XEvent *event);
 static void handleMotionNotify(XEvent *event);
 static void handleVisibilityNotify(XEvent *event);
 static void handle_inotify_events(void);
+static void handle_selection_clear(XSelectionClearEvent *event);
 static void wdelete_death_handler(WMagicNumber id);
 
 
@@ -274,6 +275,10 @@ void DispatchEvent(XEvent * event)
 #endif
 		break;
 
+	case SelectionClear:
+		handle_selection_clear(&event->xselectionclear);
+		break;
+
 	default:
 		handleExtensions(event);
 		break;
@@ -1886,3 +1891,17 @@ static void handleVisibilityNotify(XEvent * event)
 		return;
 	wwin->flags.obscured = (event->xvisibility.state == VisibilityFullyObscured);
 }
+
+static void handle_selection_clear(XSelectionClearEvent *event)
+{
+	WScreen *scr = wScreenForWindow(event->window);
+
+	if (!scr)
+		return;
+
+	if (event->selection != scr->sn_atom)
+		return;
+
+	wmessage(_("another window manager is replacing us!"));
+	Shutdown(WSExitMode);
+}
diff --git a/src/main.c b/src/main.c
index 297f3ab6..b68c5b6f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -435,6 +435,7 @@ static void print_help(void)
 	puts(_("The Window Maker window manager for the X window system"));
 	puts("");
 	puts(_(" -display host:dpy	display to use"));
+	puts(_(" --replace		replace running window manager"));
 	puts(_(" --no-dock		do not open the application Dock"));
 	puts(_(" --no-clip		do not open the workspace Clip"));
 	puts(_(" --no-autolaunch	do not autolaunch applications"));
@@ -651,6 +652,8 @@ static int real_main(int argc, char **argv)
 				wPreferences.flags.noclip = 1;
 			} else if (strcmp(argv[i], "-nodrawer") == 0 || strcmp(argv[i], "--no-drawer") == 0) {
 				wPreferences.flags.nodrawer = 1;
+			} else if (strcmp(argv[i], "-replace") == 0 || strcmp(argv[i], "--replace") == 0) {
+				wPreferences.flags.replace = 1;
 			} else if (strcmp(argv[i], "-version") == 0 || strcmp(argv[i], "--version") == 0) {
 				printf("Window Maker %s\n", VERSION);
 				exit(0);
diff --git a/src/screen.c b/src/screen.c
index 10a1fc95..1f246c45 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -66,6 +66,8 @@
     |SubstructureRedirectMask|ButtonPressMask|ButtonReleaseMask\
     |KeyPressMask|KeyReleaseMask)
 
+#define REPLACE_WM_TIMEOUT 15
+
 #define STIPPLE_WIDTH 2
 #define STIPPLE_HEIGHT 2
 static char STIPPLE_DATA[] = { 0x02, 0x01 };
@@ -90,6 +92,106 @@ static void make_keys(void)
 	dDrawers = WMCreatePLString("Drawers");
 }
 
+/*
+ * Support for ICCCM 2.0: Window Manager Replacement protocol
+ * See: http://www.x.org/releases/X11R7.6/doc/xorg-docs/specs/ICCCM/icccm.html
+ *
+ * Basically, user should be able to dynamically change its window manager; this is done
+ * cooperatively through a special Selection ("WM_Sn" where 'n' is the X screen number)
+ *
+ * This function does 2 things:
+ *  - it checks if this selection is already owned, which means that another window
+ * manager is running. If it is the case and user specified '--replace' on the command
+ * line, then it asks the WM to shut down;
+ *  - when ok, it sets the selection ownership to ourself, so another window manager
+ * may ask us to shut down (this is handled in "event.c")
+ */
+static Bool replace_existing_wm(WScreen *scr)
+{
+	char atomName[16];
+	Window wm;
+	XSetWindowAttributes attribs;
+	XClientMessageEvent event;
+	unsigned long current_time;
+	int ret;
+
+	/* Try to acquire the atom named WM_S<screen> */
+	ret = snprintf(atomName, sizeof(atomName), "WM_S%d", scr->screen);
+	if (ret < 0 || ret == sizeof(atomName)) {
+		werror("out of memory trying to allocate window manager selection atom for screen %d", scr->screen);
+		return False;
+	}
+
+	scr->sn_atom = XInternAtom(dpy, atomName, False);
+	if (! scr->sn_atom)
+		return False;
+
+	/* Check if an existing window manager owns the selection */
+	wm = XGetSelectionOwner(dpy, scr->sn_atom);
+	if (wm) {
+		if (!wPreferences.flags.replace) {
+			wmessage(_("another window manager is running"));
+			wwarning(_("use the --replace flag to replace it"));
+			return False;
+		}
+
+		attribs.event_mask = StructureNotifyMask;
+		if (!XChangeWindowAttributes(dpy, wm, CWEventMask, &attribs))
+			wm = None;
+	}
+
+	/* for our window manager info notice board and the selection owner */
+	scr->info_window = XCreateSimpleWindow(dpy, scr->root_win, 0, 0, 10, 10, 0, 0, 0);
+
+	/* Try to acquire the selection */
+	current_time = CurrentTime;
+	ret = XSetSelectionOwner(dpy, scr->sn_atom, scr->info_window, current_time);
+	if (ret == BadAtom || ret == BadWindow)
+		return False;
+
+	/* Wait for other window manager to exit */
+	if (wm) {
+		unsigned long wait = 0;
+		unsigned long timeout = REPLACE_WM_TIMEOUT * 1000000L;
+		XEvent event;
+
+		while (wait < timeout) {
+			if (!(wait % 1000000))
+				wmessage(_("waiting %lus for other window manager to exit"), (timeout - wait) / 1000000L);
+
+			if (XCheckWindowEvent(dpy, wm, StructureNotifyMask, &event))
+				if (event.type == DestroyNotify)
+					break;
+
+			wusleep(100000);
+			wait += 100000;
+		}
+
+		if (wait >= timeout) {
+			wwarning(_("other window manager hasn't exited!"));
+			return False;
+		}
+
+		wmessage(_("replacing the other window manager"));
+	}
+
+	if (XGetSelectionOwner(dpy, scr->sn_atom) != scr->info_window)
+		return False;
+
+	event.type = ClientMessage;
+	event.message_type = scr->sn_atom;
+	event.format = 32;
+	event.data.l[0] = (long) current_time;
+	event.data.l[1] = (long) scr->sn_atom;
+	event.data.l[2] = (long) scr->info_window;
+	event.data.l[3] = (long) 0L;
+	event.data.l[4] = (long) 0L;
+	event.window = scr->root_win;
+	XSendEvent(dpy, scr->root_win, False, StructureNotifyMask, (XEvent *) &event);
+
+	return True;
+}
+
 /*
  *----------------------------------------------------------------------
  * alreadyRunningError--
@@ -523,6 +625,13 @@ WScreen *wScreenInit(int screen_number)
 	CantManageScreen = 0;
 	oldHandler = XSetErrorHandler(alreadyRunningError);
 
+	/* Do we need to replace an existing window manager? */
+	if (!replace_existing_wm(scr)) {
+		XDestroyWindow(dpy, scr->info_window);
+		wfree(scr);
+		return NULL;
+	}
+
 	event_mask = EVENT_MASK;
 	XSelectInput(dpy, scr->root_win, event_mask);
 
@@ -616,11 +725,6 @@ WScreen *wScreenInit(int screen_number)
 	/* create GCs with default values */
 	allocGCs(scr);
 
-	/* for our window manager info notice board. Need to
-	 * create before reading the defaults, because it will be used there.
-	 */
-	scr->info_window = XCreateSimpleWindow(dpy, scr->root_win, 0, 0, 10, 10, 0, 0, 0);
-
 	/* read defaults for this screen */
 	wReadDefaults(scr, w_global.domain.wmaker->dictionary);
 
diff --git a/src/screen.h b/src/screen.h
index 8ffb6f9a..f3fc6fbf 100644
--- a/src/screen.h
+++ b/src/screen.h
@@ -69,6 +69,7 @@ typedef struct WDrawerChain {
 typedef struct _WScreen {
     int	screen;			       /* screen number */
     Window info_window;		       /* for our window manager info stuff */
+    Atom sn_atom;		       /* window manager selection */
 
     int scr_width;		       /* size of the screen */
     int scr_height;