Dermaptera (earwigs) is a relatively small polyneopteran order with approximately 2200 described species. They are characterized by a pair of forceps, which are hardened, unsegmented cerci at the caudal end of the abdomen. In most species, males have more exaggerated forceps than females, indicating an effect of sexual selection on them. Earwigs also exhibit astonishing diversity in the number, laterality and size of both male and female genital components. This characteristic has promoted the study of postcopulatory sexual selection in several representative species. Here, previous studies of earwigs that examined pre- and postcopulatory sexual selection are reviewed in detail. Related topics included here are sexually antagonistic coevolution, evolution of laterally asymmetrical morphologies, and developmental aspects of intra-sexually dimorphic traits. A new terminology system for male genitalia is also proposed.