What is gender? More importantly, what should gender look like in the 21st century? This book brings together philosophy with insights from feminist and transgender theory to argue for a position called ‘ameliorative pluralism’ about gender: that there should be more than two genders, and that each gender term should have multiple meanings. What Gender Should Be develops an explicitly political version of conceptual engineering (the modification of our representational devices in light of our purposes) based on the work of Otto Neurath and Audre Lorde to examine and critique existing theories of gender. It further produces novel and powerful arguments against those traditions of thinking about gender that arose after the 1980s – family resemblance theories, Butlerian performativity, deflationism, scepticism, and nihilism about gender – developing each tradition in detail before suggesting that each is insufficient for thinking about and doing justice to contemporary transgender identities and politics. Instead, Matthew Cull argues that we should be pluralists about gender, developing and arguing for a position that 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.