Originally published in 1972, the twelve articles in this volume discuss various aspects of quantum mechanics that owe their origin to the work of P. A. M. Dirac. Each of the distinguished contributors reviews Dirac's work and discusses its development in some detail. Since Dirac's work ranged widely, the resulting volume constitutes a valuable survey of the state of quantum mechanics. A small part of the book contains personal reminiscences of Dirac in Cambridge and of his early visits to the USA and gives a historical account of the development of quantum mechanics during the decade 1924–1933, aptly termed 'the golden age of theoretical physics'.