These works, as the sub-title makes clear, are unfinished sketches for Philosophical Investigations, possibly the most important and influential philosophical work of modern times. The ‘Blue Book’ is a set of notes dictated to Witgenstein’s Cambridge students in 1933-1934: the ‘Brown Book’ was a draft for what eventually became the growth of the first part of Philosophical Investigations. This book reveals the germination and growth of the ideas which found their final expression in Witgenstein’s later work. It is indispensable therefore to students of Witgenstein’s thought and to all those who wish to study at first-hand the mental processes of a thinker who fundamentally changed the course of modern philosophy.