Reflecting a sea change in how empirical research has been conducted over the past decade, Theory of Agnostic Statistics is a foundational text that develops a formalization of statistical theory for the social and health sciences without invoking strong modeling assumptions. The book represents the first unified, book-length treatment of probability theory, statistical inference and nonparametric identification for applied topics (including missing data and causal inference). We provide a formal justification and a cogent argument for the use of agnostic statistics, a perspective on empirical research that implies minimal assumptions and emphasizes credible inference. We believe that our book is uniquely suited to teach readers the foundat...