Published online by Cambridge University Press: 30 March 2016
Rather than review β Cepheids, this paper will address the issue that β Cephei variability is only a readily detectable tip of a much larger iceberg of variability among β stars. This variability being widespread, it becomes crucial to differentiate β Cepheids from other variable subgroups by observational criteria if one is ever to make physical inferences concerning the instability mechanism involved. Shobbrook (1978) has raised this point indirectly in discussing the importance of defining the width of the instability strip: if the strip is narrow, the pulsational instability is more likely to arise in the stellar core; if it is wide, it is probably excited in the envelope. Enormous efforts have gone into delineating the evolutionary and HR-D confines of ß Cepheids. In this paper it will be suggested that the situation is more complicated than the traditional outlook holds.