Abstract: Recently, much attention has been focussed on optical switches, which play a critical role in high speed data transmission. With the innovations in device design and fabrication, it is now possible to produce optical switches that consume low power, while being high speed and easy to integrate. In this paper, a thermo-optic switch with ultra-low power as low as 540mW, an ultra-fast electro-optic switch, and an all-optical switch with response times as fast as 4ns and 25ps, respectively,are first reviewed.Emphasis is put on the analysis and solutions to the problems involved.The main considerations in building a switch array are then explored and the future trends of optical switches envisaged.