Reproductive Character Displacement (RCD) has long been of interest to evolutionary biologists because of its association with speciation and reproductive isolation. Most studies of RCD focus on only a single species; however, when information about the evolutionary responses of two species is available, a possible pattern emerges: RCD often appears to be asymmetrical. Possible causes of displacement asymmetries are varied and include asymmetrical costs of hybridization, constraints, the effects of relative abundance, and extinction. Yet in spite of this variety, further study may show that asymmetries in RCD contain important clues about the interactions pf species in contact zones.