Observational aspects of multiperiodicity in the β Canis Majoris stars

β Canis Majoris-type variable stars are discussed and observational data is given. Three classes of variables are discussed. They are Class I variables which have only one short period, Class II variables which are all members of binary systems and have one short period which appears to be superimposed on a longer variation attributable to orbital motion and class III variables having two or more short periods. This last group are truly multiperiodic and are not all members of binary systems. Various theories of multiperiodicity are also discussed. (B.D.)