What does a chess master think when he prepares his next move? How are his thoughts organized? Which methods and strategies does he use by solving his problem of choice? To answer these questions, the author did an experimental study in 1938, to which famous chessmasters participated (Alekhine, Max Euwe and Flohr). This book is still useful for everybody who studies cognition and artificial intelligence. The studies involve participants of all chess backgrounds, from amateurs to masters. They investigate the cognitive requirements and the thought processes involved in moving a chess piece. The participants were usually required to solve a given chess problem correctly under the supervision of an experimenter and represent their thought-processes vocally so that they could be recorded. De Groot found that much of what is important in choosing a move occurs during the first few seconds of exposure to a new position. Four stages in the task of choosing the next move were noted. The first stage was the 'orientation phase', in which the subject assessed the situation and determined a general idea of what to do next. The second stage, the 'exploration phase' was manifested by looking at some branches of the game tree. The third stage, or 'investigation phase' resulted in the subject choosing a probable best move. Finally, in the fourth stage, the 'proof phase', saw the subject confirming with him/herself that the results of the investigation were valid. De Groot concurred with Alfred Binet that visual memory and visual perception are important and that problem-solving ability is of paramount importance. Memory is particularly important, according to de Groot (1965), in that there are no 'new' moves in chess and so those from personal experience or from the experience of others can be committed to memory.