A method for fabricating optical MEMS (optical Micro-Electro-Mechanical Systems or Micro-Opto-Electro-Mechanical Systems (MOEMS)) is described. The basic process involves deposition and patterning of a sacrificial spacer layer and a combined moulding and photolithography step. The method described allows the fabrication of micromechanical elements incorporating micro-optical structures such as lenses (diffractive or refractive), gratings (for polarisers or resonant filters), waveguides or other micro-optical relief structures fabricated by UV-curing replication processes.