The sensitivity of MEMS devices to radiation is reviewed, with an emphasis on radiation levels representative of space missions. While silicon and metals generally do not show mechanical degradation at the radiation levels encountered in most missions, MEMS devices have been reported to fail at doses of as few krad, corresponding to less than one year in most orbits. Radiation sensitivity is linked primarily to the impact on device operation of radiation-induced trapped charge in dielectrics, and thus affects most strongly MEMS devices operating on electrostatic principles. A survey of all published reports of radiation effects on MEMS is presented. The different sensing and actuation physical principles and materials used in MEMS are compared, leading to suggested was to increase radiation tolerance by design, for instance by choice of actuation principle or by electrical shielding of dielectrics.