The Harvard philosopher Donald C. Williams (1899-1983) was key figure in twentieth-century philosophy, but underappreciated. He played a crucial role in reviving metaphysics at a time when other philosophers would ridicule, criticise, and commit it to the flames. Today, as metaphysics thrives, his work is highly relevant and widely studied. But his publications have been scattered through journals and out-of-print books and some of his most important ideas were left unpublished. A. R. J. Fisher brings together for the first time six of his influential articles and six previously unpublished papers on such metaphysical topics as universals, essence, necessity, time, and time travel.