Ludwig Wittgenstein is widely regarded as the most important philosopher of the twentieth century, and the Tractatus Logico-Philosophicus is the only book-length work of philosophy he published in his lifetime. Together, these two facts convey some idea of the power this work has exerted over the minds of other philosophers and over the discipline itself. In this book, Wittgenstein claims no less than to have solved all the problems of philosophy, and for a work with such a small page count, it is astonishing in its ambition. It manages to offer a radical new theory of logic, along the way addressing such problems as the foundations of mathematics, solipsism, the nature of ethics and art, and even free will.