Anumber of recent studies have suggested that the rapid evolution of genes involved in sexual reproduction is driven by conflict between the sexes. Such genes include the ones that have a role in mating behavior, postmating gamete interactions, and fertilization (i.e., sex-related genes). However, in many cases an alternative scenario with males coadapting to female-driven changes appears as an equally likely one. Studies on the molecular evolution of sex-related genes have mainly focused on males, with few exceptions. We suggest that the combined analysis of intraspecific polymorphism and interspecies divergence will allow to make predictions on whether sex-related genes evolution is driven by conflict or coadaptation between the sexes. Such approach, made possible by rapid accumulation of DNA sequence information, will benefit from studies designed to identify male and female gene products that interact with each other during mate signaling, fertilization, and postzygotic development.