Liquid crystal devices to perform optical switching, filtering and to build optical crossconnects for wavelength division multiplexed optical communication systems are reviewed. Basic working principle of both devices already commercialised and those ones still at laboratory stage reported in the recent scientific literature are described. Devices based on liquid crystals and those ones made by using alternative technologies (MEMS, lithium niobate, semiconductors) are compared in terms of advantages and disadvantages. Technology issues to fabricate liquid crystal based photonic devices are discussed. Recent results of both free-space and waveguided based liquid crystal optical devices along with novel device concepts using optical channel waveguides are reported.