This chapter discusses the need for a good power factor and how it can be achieved by power factor correction or other means. A traditional boost converter type of power factor correction circuit, where the output is a fixed high voltage, is described first. This circuit could be used in combination with a buck constant current switching circuit to drive a string of light-emitting diodes. A more integrated boost stage and linear regulator, with a constant current output, is described. Other more exotic schemes are described, with one design example.