This edited volume gives an overview of the concepts and methods used in current research in quantum logic, viewed both as an operational physical theory and in terms of purely mathematical structure. Far from being simply a collation of research papers, it consists of 11 specially commissioned essays that, taken together, provide both an introduction to quantum logic and an overview of current research in this subject. The contributors, who include some of the most distinguished names in the field, discuss topics ranging from the algebraic theory of orthomodular lattices to recent applications of category-theoretic methods and connections with theoretical computer science. Moreover, an historical overview of the field and an extensive citation and concept index are included. Audience: This volume, dedicated to D.J. Foulis in honour of his seminal contributions to quantum logic, should interest pure mathematicians, theoretical physicists, computer scientists and philosophers of science.