Between them, the movements of Logical Positivism and Existentialism dominated philosophy in Europe for much of the 20th century, and the influence they exerted can still be felt today. In this publication Frederick Copleston provides a detailed and objective introduction to these two highly controversial areas of recent thought. Originally written in 1956, and revised in 1972, it explores the work of many of the most important thinkers of the 20th century, including Ayer, Wittgenstein, Heidegger, Sartre and Camus.