In virtue of their capacity for political agency, political agents can possess special rights, powers, and responsibilities, such as rights to political participation and freedom of speech. Traditionally, political theorists have assumed that only cognitively unimpaired adult humans are political agents, and thus that only those humans can be the bearers of these rights, powers, and responsibilities. However, recent work in animal rights theory has extended the concept of political agency to nonhuman animals. In this article, I develop an account of political agency that identifies the capacities that one must possess to be a political agent and captures the fact that political action is a distinctive type of action. Crucially, this account makes sense of the standard assumption that only some humans count as political agents, and explains why few nonhuman animals, human infants, and severely cognitively impaired humans are likely to possess the capacity for political agency. I go on to reject the view, recently advanced by Sue Donaldson and Will Kymlicka, that nonhuman animals can be ‘nonintentional political agents’. I conclude by suggesting that most nonhuman animals, as well as human infants and humans with severe cognitive impairments, cannot straightforwardly be assigned rights to political participation.