In his brilliant and tragically brief career, Kenneth Craik anticipated certain ideas in biology and psychology which have since his death found wide acceptance. Craik was one of the first to realise that the machines of his and our day share some of the principles of functioning with brains. Kenneth Craik was killed in an accident in 1945 and left a large number of unpublished papers, a selection of which have here been sorted and edited by Dr Stephen L. Sherwood. The selection includes the draft for a book on the 'Mechanism of Human Action' with important ideas on learning, thinking, decision-making and on models of brain mechanism. There is also fascinating material on the measurement of perception, sensory physiology and the relationship of nervous function to machines. There are some philosophical discussions and a few introspective comments.