A cataclysmic binary is a close binary system consisting of a white dwarf primary and an orange or red (K- or M-type) main-sequence or giant secondary, in which matter flows from the secondary toward the primary. In most cases, the stripped hydrogen-rich gas enters an accretion disk around the white dwarf and may subsequently fall onto the condensed star to ignite violently in a fusion reaction. Cataclysmic variables fall into two groups. The non-magnetic group, which is by far the most populous, includes U Geminorum stars (dwarf novae) and classical and recurrent novae. The much rarer, magnetic group includes AM Herculis stars and DQ Herculis stars and is distinguished by the presence of a powerful magnetic field around the primary that dramatically affects the accretion flow.