What is gender? What should gender look like in the 21st century? This book brings together philosophy with insights from feminist and transgender theory to argue for gender pluralism: that there should be more than two genders, and that each gender term should have multiple meanings. Developing an explicitly political version of conceptual engineering, What Gender Should Be contains novel and powerful arguments both against existing theories of gender such as family resemblance accounts and against gender abolition, underlining how each is insufficient for thinking about and doing justice to contemporary transgender identities and politics. Instead, Matthew J. Cull argues that we should be pluralists about gender, putting forward and advocating for a position that is more apt for contemporary transgender and feminist activism. The 21st century requires a new way of thinking about gender. What Gender Should Be sets out to provide it.