Rationality: A-Z (or "The Sequences") is a series of blog posts by Eliezer Yudkowsky on human rationality and irrationality in cognitive science. It is an edited and reorganized version of posts published to Less Wrong and Overcoming Bias between 2006 and 2009. This collection serves as a long-form introduction to formative ideas behind Less Wrong, the Machine Intelligence Research Institute, the Center for Applied Rationality, and substantial parts of the effective altruist community. Each book also comes with an introduction by Rob Bensinger and a supplemental essay by Yudkowsky.

The first two books, Map and Territory and How to Actually Change Your Mind, are available on Amazon (printed and e-book version).

The entire collection is available as an e-book and audiobook. A number of alternative reading orders for the essays can be found here, and a compilation of all of Eliezer's blogposts up to 2010 can be found here.