Sexual economics theory analyzes the onset of heterosexual sex as a marketplace deal in which the woman is the seller and the man is the buyer, with the price paid in nonsexual resources. We extend that theory to analyze same-gender contests in that marketplace, and to elaborate the idea that what the woman sells is not just sex but exclusive access to her sexual charms. Women compete on sex appeal and on the promise of exclusiveness (faithfulness), with the goal of getting a man who will provide material resources. Men compete to amass material resources, with the goal of getting a good sex partner. Female competition includes showing off her sexual charms, offering sex at a lower price than rivals, seeking to improve her physical assets (e.g., by dieting), and use of informational warfare to sully rivals’ reputations while defending her own reputation against malicious gossip. We review evidence of these patterns, including evidence that female body dissatisfaction and pathological eating patterns increase when women perceive an unfavorable sex ratio (i.e., shortage of eligible men). Men compete in groups to amass resources, so men see other men not just as sexual rivals but also as coalition partners. Male homophobia is often not about sex but rather invokes the stereotype that a homosexual man will not be an effective coalition partner. Misunderstandings about whether sex or exclusivity is the central commitment can complicate marital adjustment for couples.