Mechanical　actuators,　which　convert　external　stimuli　to　motion,　play　a　significant　role　in　medical　devices,　automobiles,　aircrafts,　and　robots.　With　their　associated　advantages　of　large　shape　change,　high　force,　and　high　efficiency,　phase　transitions　are　among　the　most　important　driving　forces　in　actuation.　There　are　many　phase-transition　materials　suitable　for　actuators,　and　many　of　them　find　applications　in　the　real　world.　In　this　Tutorial,　we　review　some　typical　phase-transition　driving　materials　for　actuators,　including　shape　memory　alloys,　piezoelectric　ceramics,　vanadium　dioxide,　liquid　crystal　elastomers,　hydrogels,　shape　memory　polymers,　and　paraffin　wax.　The　phase-transition　mechanisms　of　the　materials　are　introduced,　and　the　design　principles　and　related　applications　of　the　associated　actuators　are　discussed.