This article provides a critical overview of research on human rationality. Rationality research poses a number of unusual challenges to psychologists. For one, it is unusually interdisciplinary and involves research conducted in adjacent disciplines (e.g., economics, education, communication, computer science and philosophy), not all of which are accessible with psychological training. What underlies this diversity, however, is an arguably even more unusual feature: the fact that even purely descriptive research, focused on what we actually do, cannot proceed without reference to normative considerations, that is, considerations of what we ought to do. Empirical results can thus only be understood with some understanding of the relevant norms of rationality. This article introduces the range of relevant frameworks, followed by examples of the different ways these frameworks are put to use. The bulk of the article then surveys research findings on human rationality across the core areas of (probability) judgment, reasoning, decision-making, and argumentation. Two final sections provide cross-cutting themes, one on the contrast (and interrelationship) between individual and collective rationality and one on the unique challenges of linking rationality research to real-world concerns.