This document contains 22 papers presented at an international congress on mathematical education. An introductory report describes the work of the theme group, "Mathematics for All," motivated by the move to universal elementary education in developing countries, the move to universal secondary education in industrialized countries, and the experience with worldwide curriculum developments such as the "new math" movement. The papers are introduced briefly, with the conclusion that there are at least three very different dimensions which contribute to and affect the difficulty of teaching mathematics effectively to the majority of students, namely, the influences of social and cultural conditions, of the organizational structure of the school system, and of classroom practice and interaction. The papers are then presented in three categories: (1) "Mathematics for All--General Perspectives" (7 papers); (2) "Problems and Developments in Industrialised Countries" (10 papers); and (3) "Problems and Developments in Developing Countries" (5 papers). The topics range from broad descriptions and analyses to specific research findings and classroom practices. (MNS)