As very large scale integration technology advances toward higher complexity and density, future generation computing and communications systems will operate at speeds of several hundred megahertz or even gigahertz. In many cases, the capability of the interconnections within these systems to support the required speeds and densities will be a formidable challenge. Multichip-module (MCM) technology is one approach to overcome some of the interconnection bottlenecks, but even such an advanced packaging system has limitations, especially for very high speed complex systems. Optical interconnections offer the potential for improved performance in terms of large bandwidth, noise and crosstalk immunity, lower power dissipation, and large fan-out capability. We discuss the use of optical interconnections within multichip modules. We consider three specific applications-input/output access to the MCM, global signal distribution, and chip-to-chip interconnects-and discuss both free-space and guided-wave implementations of optical interconnects.