Polymer materials, including elastomers, plastics and fibers, are being actively used for MEMS sensors and actuators. Polymer materials provide many advantages in terms of cost, mechanical properties, and ease of processing. In addition, polymers are being investigated for displays, memory, and circuitry. However, the incorporation of polymers for structural or functional purposes in MEMS systems raises new issues and challenges. This article provides a comprehensive review of the recent state of the art of polymer based MEMS-including materials, fabrication processes, and representative devices, including microfluidic valves and tactile sensors. Frequently used materials are reviewed, including polydimethylsiloxane (PDMS), parylene, nanocomposite elastomers, and SU-8 epoxy.