OPEN LOOK or OpenLook was an early graphical user interface (GUI) specification developed by Sun Microsystems and AT&T in the early 1990s for UNIX workstations. It had its origins in SunOS 2.1, SunView, and Sun's Motorola 68000–based UNIX workstations. OpenLook was distinguished by its oval-shaped buttons, triangle pull down menus and pushpins which allowed dialog boxes and palettes to stay visible. Because it was a specification at the user level, it could actually be implemented in different ways underneath — using X Window System or Sun's NeWS toolkit. The specification was a collaboration between Sun and AT&T, which had an alliance back to develop UNIX and graphical toolkits. OpenLook had a usable pallete of 256 colours.

In the early 1990s, its main competitor was the OSF Motif GUI or the vanilla X Window System twm window manager and Athena widgets. At the time, Motif was backed by the rest of the workstation industry, such as IBM, Hewlett-Packard, and Digital Equipment Corporation.

The X Window System implementation was the Open Look Intrinsics Toolkit, or OLIT. This was built on the XtIntrinsics toolkit that is part of X Windows. In 1990, UNIX Systems Laboratories inherited OLIT from AT&T along with UNIX. Not long after, the codebase for OLIT diverged when Sun and USL took different paths in further enhancing the toolkit.

Sun continuted to enhance the look and feel of OLIT to make it more consistent with its OpenWindows, its non-XtIntrinsics Open Look implementation.

In an attempt to create an API to make applications GUI independent, USL developed the awkwardly named MoOLIT or Motif Openlook Intrinsics Toolkit, which was kept OLIT API, but allowed users to choose which GUI they wanted at runtime. The source to MoOLIT was licensed by MJM Software, who ported it to several other UNIX platforms. It was used for several years, almost exclusively by AT&T and Lucent Technologies, who wanted to give their existing Open Look applications a Motif look and feel. It was not widely used elsewhere.

Shortly after the industry had made its intentions clear, OpenLook was dropped by Sun in favor of Common Desktop Environment and Motif.