Pericyclic reactions constitute a major strand of organic chemistry, including such commercially important synthetic reactions as the Diels-Alder reaction. Reactions such as these are characterised by their predictable stereochemistry and cyclic transition structures. This primer reviews these reactions in order to explain their theoretical basis via correlation diagrams. It also shows students how to recognize the different types of pericyclic reaction, their mechanisms, and their applications to organic synthesis. The text is part of the renowned Oxford Chemistry Primer series, which provides focused introductions to a range of important topics in chemistry. The series has been refreshed and updated to suit the needs of today's students and instructors. The rigorous, yet accessible, the texts include cutting-edge examples and relevant applications. Pedagogical features provided in the primers--including questions at the end of every chapter, diagrams, margin notes, suggestions for further reading, and an expansive glossary--encourage active learning and promote understanding.