When paraffin wax melts it exhibits a large, relatively incompressible volume expansion. This can be used in microactuators for strong and large displacements, a rare combination among actuators. Furthermore, paraffin is inexpensive, inert and environmentally friendly, as well as easily processed and actuated. Together, these properties give paraffin actuators great potential for use in both low-cost and high-performance applications. In microfluidics, the miniaturization of various analysis systems decreases the volumes of samples and reagents needed, as well as the analysis throughput time. Using on-chip micropumps increases the efficiency of the microfluidic system, but a challenge for such pumps is the high back-pressure associated with separation, filtration or narrower channels. The objective of this thesis is to increase the understanding of paraffin in microactuators, as well as to further explore its possibilities and limitations. The main application area has been on-chip micropumps. For low-cost applications, actuators, pumps and dispensers have been fabricated in plastics and then evaluated. The dispenser is intended for on-chip storage and dispensing of liquids in a lab-on-a-chip that could be used in, e.g., point-of-care testing (POCT). For high-performance applications, metallic actuators, pumps and dispensers have been accomplished. The micropump is the world’s strongest mechanical micropump in sub-cubic centimetre size, capable of pressures of above 5 MPa. Possible applications are strong microhydraulics, on-chip chromatography, or medical microdosage systems. A limitation of paraffin is the relatively slow thermal actuation. In this thesis the thermal properties have also been turned into an advantage: Directional solidification is used to accomplish multiple stable states of the actuator displacement, withheld without any power consumption. For the future, the high-pressure capability may be improved by new designs. Optimization of speed and power consumption can be made by further work on modelling as well as on drive and control of the heating.