The application of a magnetic field to semiconductor crystal growth melts in order to control melt flow and thereby dopant distribution on both macro- and micro-scales is reviewed. Most emphasis is given to Czochralski and LEC growth and the generation of transverse, axial and configured fields is described. Theories predicting flow and segregation in the presence of a magnetic field are outlined and compared with a wide range of published experimental data relating principally to silicon, gallium arsenide and indium phosphide. The technically-important case of oxygen concentration control in Czochralski is considered in detail, including some previously unpublished data. Finally, the published literature on the use of a magnetic field in non-Czochralski growth configurations is reviewed.