Microengineering started as a field of study of devices which exploited the mechanical properties of silicon. In particular, sensors, of which pressure sensors and accelerometers are the two greatest commercial successes to date, became a very popular field of study. The subject of actuation in microengineering is now attaining equal importance with that of sensors; examples of commercially exploited devices include inkjet printer nozzles, micromirrors, pumps, valves, bimorphs and gyroscopes. This paper reviews the subject of actuation in microengineering, in terms of the factors to consider, the mechanisms and materials involved, example structures and a comparison of the advantages and drawbacks associated with each actuation system.