Past, Present and Future, first published in 1867, is the magnum opus of Arthur Norman Prior (1914-1969). Prior was the founding father of tense-logic: Past, Present, and Future presents his tense-logic as a powerful and precise formalism for the systematic study of the temporal aspects of reality. The book was the summation of a decade of work on tense-logic following Prior's John Locke lectures at the University of Oxford in 1956, subsequently published in 1957 as Time and Modality. Among a wide range of topics, Past, Present and Future investigates the idea of branching time that had earlier been suggested by Saul Kripke. It includes several philosophical investigations of time, from a discussion of McTaggart's paradox, the Master Argument of Diodorus, time and existence, problems regarding determinism and future contingency. Prior's discussion of these matters invited a broad scope of ancient and medieval philosophers into the modern discussion in the philosophy of time. Prior was spearheading a revolution in analytic philosophy. Unfortunately, Prior's choice of Polish logical notation has limited its influence. This new edition employs modern notation, making it accessible to a new generation of philosophers and logicians. It includes a new preface a postscript by the editors, which can serve as an introduction to this landmark work of analytic philosophy.