We review a polymeric waveguide technology developed to produce affordable high-performance optical components that address the needs of both the telecom and the datacom industries. We engineer advanced organic polymers that can be readily made into planar single- mode, multimode, and micro-optical waveguide structures of controlled numerical apertures and geometries. These materials are formed from highly crosslinked acrylate monomers with specific linkages that deter- mine properties such as flexibility, toughness, optical loss, and environ- mental stability. These monomers are intermiscible, providing for precise continuous adjustment of the refractive index over a wide range. In poly- mer form, they exhibit state-of-the-art loss values, suppressed polariza- tion effects, and exceptional stability, enabling their use in a variety of demanding applications. Waveguides are formed photolithographically, with the liquid monomer mixture polymerizing upon illumination in the UV via either mask exposure or laser direct writing. A wide range of rigid and flexible substrates can be used. The devices we describe include a va- riety of passive and thermo-optically active elements that achieve a va- riety of coupling, routing, and filtering functionalities. These devices can be either individually pigtailed and packaged components or they can be part of a massively parallel photonic integrated circuit on the multichip module (MCM), board, or backplane level. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)01003-5)