The current fiber optical communication system has evolved into a complicated multi-wavelength system with the deployment of Wavelength Division Multiplexing (WDM) networks. Many innovative technologies are desired to materialize its vast capacities and promises. MEMS technology has recently emerged as a competitive candidate to solve many technical challenges encountered in current WDM networks. Its applications have spanned from large scale optical switch fabrics such as optical cross-connects, optical add/drop multiplexers, to a large variety of active and passive optical components for transmission networks, such as tunable lasers and filters, dispersion compensation devices, amplifier gain equalizers, polarization controllers, and many others. In this paper we will discuss the current development status, promises and challenges, and the future prospects of MEMS technologies for optical communication, with a primary focus on MEMS-based optical cross-connects.