In the half century since the Philosophical Investigations was published, and the eighty years since the first review of the Tractatus, Wittgenstein's writing not only inspired two of the principal philosophical movements of the twentieth century – the Vienna Circle and Oxford ordinary language philosophy – but also had a far-reaching influence on an extraordinarily wide range of philosophers and researchers in almost every field of the humanities and social sciences. While the other leading figures of logical empiricism and ordinary language philosophy have receded into the historical background, Wittgenstein is one of a small group of twentieth-century philosophers who have become canonical figures, both within and beyond the world of professional philosophy. In an end-of-the-century poll, professional philosophers in the USA and Canada were asked to name the five most important books in philosophy in the twentieth century. The Philosophical Investigations came first, and the Tractatus fourth. The Philosophical Investigations was ‘cited far more frequently than any other book and was listed first on more ballots … the one crossover masterpiece in twentieth-century philosophy, appealing across diverse specializations and philosophical orientations’. Wittgenstein has also become an iconic figure: he is the only philosopher to appear on Time's turn-of-the-millennium list of the 100 ‘most important people of the century’ and has been the subject of biographies, novels, poetry, films, and artworks.