The use of microwave irradiation has become a common heat source in organic chemistry. Inspired by this enormous success, the use of microwave irradiation is also increasingly studied for polymerization reactions. The present review discusses developments in this rapidly growing field of research. The main areas in which the use of microwave irradiation has been explored in the recent years are step-growth polymerizations, ring-opening polymerizations as well as radical polymerizations. These different areas will be addressed in detail, whereby special attention will be given to observed improvements resulting from the use of microwave irradiation as well as the occurrence of non-thermal effects.