The studies of thinking begun by Galton and continued in various ways by Binet, Piaget, Wertheimer, Selz, vygotsky. and others frequently touched on the mental abilities one uses in doing mathematics. Many of the tasks used in the studies were mathematical in nature, but even when they were not, the kinds of complex thought these psychologists identified often seemed to mathematics educators to be linked to mathematical performance. Psychological research into mathematical thinking has complemented and extended the insights mathematicians have had about how they work. It has not, however, had as pervasive an influence on research in mathematics education as studies of teaching and learning have had.