Microelectromechanical Systems (MEMS) is a rapidly emerging field of research in which batch fabrication processes are used to construct miniature devices. MEMS devices are particularly well suited to optical applications. Foundry microfabrication offers a substantial cost advantage for prototype system development. In this research, foundry MEMS processes are used to fabricate low-cost deformable mirror systems (MEM-DMs) for adaptive optics. The challenges and design trades associated with fabrication of continuous and segmented deformable mirrors in foundry processes are examined in detail. Micromirror surface figure is shown to be critically important. Beam steering and optical aberration correction experiments conclusively demonstrate the potential of low-cost MEM-DMs. The prototype MEM-DM systems are approximately 1/ 500th the cost of conventionally manufactured deformable mirrors. An innovative direct digital control scheme further reduces adaptive optic system cost by eliminating the digital to analog converter typically required for each controlled element. In addition to the MEM-DMs, other MEMS devices are shown. The thermally actuated piston micromirrors offer greater deflections for operation at longer optical wavelengths. Other MEMS devices examined include a series of tilting mirrors, pressure gauges, test structures, electrostatic scratch drive actuated rotors, and a new type of electrostatic cantilever motor with lateral motion output.