Strong reciprocal relationships have long been suspected between mating systems and sexual selection, and so different angles of discussion can be pursued to investigate these relationships. In this essay, mating systems are regarded as one of the factors that may influence the strength and consequences of sexual selection. The ungulates show a wide variety of mating systems, and though most ungulate species are polygynous, male mating tactics range from non-territorial males courting individual estrous females, to both female-defense harem systems and resource-defense territorial systems, and to leks. It is thus interesting to focus on this group to investigate the scope for development of sexual selection in relation to various mating tactics. Based on behavioural ecology and sexual selection theories, it is possible to propose several predictions concerning mechanisms of competition over mates and sexually selected traits favoured by each ungulate mating tactic. The aim of this essay is to review the main sexually selected traits reported in ungulate studies, with special reference to the Cervidae, the Bovidae and the Antilocapridae, and to discuss the fit of them with the theoretical predictions.