Application's icon can be used for various purposes by the window managers on Windows and Unix: it can identify the application when it is minimized to the desktop, for example, or it can be displayed next to application's name in the taskbar, etc. Unfortunately, Gtk+ 1.2.x for Win32 does not support setting the icon programmatically. But on other platforms one should do this: realize(); $gdkwin = $win->window; list($pixmap, $mask) = gdk::pixmap_create_from_xpm($gdkwin, null, "icon.xpm"); $gdkwin->set_icon(null, $pixmap, $mask); ?>]]> The first parameter to set_icon() is a GdkWindow which can serve as an icon for the window when it is minimized. Only certain window managers support this functionality, though.