David Lewis's work is among the most influential in many areas of contemporary philosophy, but much of his influence has been as a “philosopher's philosopher”: his main impact to date has been on the work of other professional philosophers. His work deserves a broader audience, since it is full of thought-provoking ideas, breadth of vision, a clear and incisive treatment of issues and plain good sense. He deals in a straightforward and unpretentious manner with many of the deepest philosophical issues, and his picture of the world and our place in it is one that deserves to be widely known.

Lewis's work covers topics in many of the central areas of philosophy: metaphysics, philosophy of language, philosophy of mind, decision theory, philosophy of mathematics, epistemology, philosophical logic, philosophy of science, value theory and many others. Despite this, his views have a unity to them. A comprehensive philosophical system emerged gradually from Lewis's writings, somewhat of a rarity in Anglo-American philosophy in the second half of the twentieth century. It emerged somewhat unexpectedly, even for Lewis. “I should have liked to be a piecemeal, unsystematic philosopher, offering independent proposals on a variety of topics. It was not to be,” he commented in the introduction to his first volume of collected papers. Indeed, many of his readers may only have a vague idea of how his views fit together, since it is possible to engage in one set of issues dealt with by Lewis without engaging very much in the others.