Polymers are ideally suited for use in microelectromechanical systems (MEMS) and microfluidic devices because of their low cost, chemical inertness, low electrical and thermal conductivity, and suitability for surface modification and compatibility with biological materials. A wide variety of polymers including parylene, polydimethylsiloxane, SU-8 resist, and hydrogels have been employed in the construction of these devices. A number of nontraditional micromachining techniques including injection molding, hot embossing, stereolithography, and traditional bulk and surface micromachining methods have been employed. This chapter discusses the polymers that are widely used in MEMS and their properties, processing methods, and applications in detail.