Shortly after it was proposed, optical micro-electromechanical systems (MEMS) was recognized as the most promising all-optical switching technology for core lightwave-communications networks. Focusing on achieving low loss, high port-count, and bit-rate transparency, this technology provides the best match for the applications of provisioning and restoration in core optical networks, without following the mislead path in the history of optical-switch development that all-optical switches need to achieve fast nanosecond switching time. Although the delay in capacity demand of long-haul optical networks has dramatically slowed down the development and commercialization of this technology, many impressive technological advances have been demonstrated as a result of intense research and development in a brief period of a few years. In this paper, we review various technologies for MEMS optical switches, and discuss their roles in optical communication networks.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.