Originally published in 1987, interest in mathematical cognition was not new in psychology. However, it was rediscovered in the 1970s under the influential work of the Genevan School. In particular, Piaget’s work on conservation, including conservation of number, profoundly influenced developmental psychologists who, working first in the Piagetian theoretical framework, began to discover a broader set of topics in mathematical cognition. In developmental psychology, the field continued to expand and covered a wide range of topics.During the same period, however, no such evolution occurred in neuropsychology, and except for some studies around the time of publication, very little had been published on acalculia and number processing disorders. However, a more general theoretical evolution occurred in neuropsychology, mainly due to increasing collaboration between clinical and experimental neuropsychologists, on the one hand and cognitive psychologists on the other. The objective of this book was to promote an evolution in the neuropsychology of calculation and number processing deficits and thus to introduce clinical and experimental neuropsychologists, as well as developmental and cognitive psychologists, to recent research and theoretical approaches that are of particular interest for the neuropsychological approach to mathematical cognition.