Assertions belong to the family of speech acts that make claims regarding how things are. They include statements, avowals, reports, expressed judgments, and testimonies - acts which are relevant across a host of issues not only in philosophy of language and linguistics but also in subdisciplines such as epistemology, metaphysics, philosophy of mind, ethics, and social and political philosophy. Over the past two decades, the amount of scholarship investigating the speech act of assertion has increased dramatically, and the scope of such research has also grown. The Oxford Handbook of Assertion explores various dimensions of the act of assertion: its nature; its place in a theory of speech acts, and in semantics and meta-semantics; its role in epistemology; and the various social, political, and ethical dimensions of the act. Essays from leading theorists situate assertion in relation to other types of speech acts, exploring the connection between assertions and other phenomena of interest not only to philosophers but also to linguists, psychologists, anthropologists, lawyers, computer scientists, and theorists from communication studies.