Originally published in 1963, The Concept of the Positron forms a detailed analysis of quantum theory. Whilst it is not as well known as Professor Hanson’s previous book, Patterns of Discovery (1958), the text has many interesting aspects. In many ways it goes further than Hanson’s earlier work in approaching the problems of theory competition and the rationality of science, topics that have since become central to the philosophy of science. It is also notable for a rigorous and forthright defence of the Copenhagen Interpretation. Taken together, the ideas presented in this book constitute a first-rate achievement in the history and philosophy of science. This paperback reissue comes with a new preface from Matthew Lund, Assistant Professor, Faculty of Philosophy and Religious Studies at Rowan University.