Diffractive optical elements easily handle tasks such as the generation of uniform arrays of beams, beam steering and focusing, and aberration correction that conventional optics alone often find difficult or impossible. Here we review the design, fabrication, and performance of DOEs for use as free-space interconnection elements in optical-computing and photonic-switching applications. Our discussion focuses on Fourier- and Fresnel-regime surface-relief structures and their microlithographic fabrication. We include two practical examples to demonstrate the potential of such optical elements.