The International Group for the Psychology of Mathematics Education (IGPME) was founded in 1976 at the Third International Congress for Mathematics Education, to promote international contacts and the exchange of scientific information in the psychology of mathematical education. The goal was to further a deeper and more correct understanding of the psychological aspects of teaching and learning mathematics and the implications thereof. This material consists of two documents. The first is a collection of approximately 70 papers classified under the following themes: (1) Concept Formation; (2) Problem Solving; (3) Language; (4) Proof; (5) Arithmetic and Algebra; (6) Ratio and Proportion; (7) Methods of Teaching; (8) Assessment; (9) Errors, (10) Discovery Learning; (11) Social Aspects; and (12) Neurophysiology. The second volume contains two of the five plenary lectures presented at the conference, a listing of the contents for the first document, and five additional conference papers. (MP)