 At the age of 24 Brouwer wrote the book Life, Art and Mysticism (Brouwer 1905), whose solipsistic content foreshadows his philosophy of mathematics. In his dissertation the foundations of intuitionism are formulated for the first time, although not yet under that name and not in their final form. In the first years after his dissertation most of Brouwer’s scientific life was devoted to topology, an area in which he is still known for his theory of dimension and his fixed point theorem. This work is part of classical mathematics; according to Brouwer’s later view, his fixed point theorem does not hold, although an analogue cast in terms of approximations can be proved to hold according to his principles.