A.N. Prior’s Past, Present and Future was published 50 years ago in 1967 and was clearly a milestone in the development of tense-logic. It is a mature and comprehensive presentation of the basic concepts, systems and issues in tense-logic. In addition it also contains a number of interesting ideas that later led to important further developments of the field. Past, Present and Future represents a culmination of Prior’s struggle with the problem of determinism (including his study of the tension between the doctrines of divine foreknowledge and human freedom). Prior’s study of the problem of determinism led him to a reconstruction of the famous Diodorean Master Argument which had for centuries been regarded as a strong argument in favour of determinism. In his further analysis of the problem, he made extensive use of tense-logic and the idea of branching time suggested to him by Saul Kripke. However, in Past, Present and Future Prior also stresses that time as such should not simply be understood in terms of branching time diagrams. Such diagrams should be seen not as direct representations of time but rather as figures helpful for understanding a deeper tense-logical structure.