The role of the perineal muscles in erection physiology is currently controversial. Specifically, confusion persists as to the function, if any, the ischiocavernosus (IC) and bulbospongiosus (BS) muscles possess in nonejaculatory erections. An extensive review of the evidence for and against such an erectile role across five orders of mammalian species indicates that the IC muscles create rigidity by producing suprasystolic intracavernous pressures. The BS muscles, on the other hand, are primarily involved in expelling semen during ejaculation. Beckett and coworkers were the first to demonstrate a clear relationship between IC muscle contractions, suprasystolic intracavernous pressures and rigidity. This Beckett model is used to differentiate an erect phase from a rigid erect phase in the erection cycle. The involvement of these muscles in sleep-related erection physiology is also reviewed. Clinical implications and directions for future research are discussed.