The Proceedings of PME-XI has been published in three separate volumes because of the large total of 161 individual conference papers reported. Volume I contains four plenary papers, all on the subject of "constructivism," and 44 commented papers arranged under 4 themes. Volume II contains 56 papers (39 commented; 17 uncommented) arranged under 9 themes. Volume III contains 53 papers arranged under 17 themes, and 4 Research Agenda Project papers. Due to space limitations, the subject content of these volumes will be represented by listing the 30 themes used to categorize the papers. Volume I: (1) Affective Factors in Mathematics Learning; (2) Algebra in Computer Environments; (3) Algebraic Thinking; (4) Fractions and Rational Numbers; Volume II: (5) Geometry in Computer Environments; (6) In-Service Teacher Training; (7) Mathematical Problem Solving; (8) Metacognition and Problem Solving; (9) Ratio and Proportion; (10) Number and Numeration; (11) Addition and Subtraction; (12) Rationals and Decimals; (13) Integers; Volume III: (14) Cognitive Development; (15) Combinatorics; (16) Computer Environments; (17) Disabilities and the Learning of Mathematics; (18) Gender and Mathematics; (19) Geometry; (20) High School Mathematics; (21) Effect of Text; (22) Socially Shared Problem Solving Approach; (23) Didactic Engineering; (24) Curriculum Projects; (25) Affective Obstacles; (26) Instructional Strategies; (27) Measurement Concepts; (28) Philosophy, Epistemology, Models of Understanding; (29) Pre-Service Teacher Training; (30) Teritary Level. Each volume contains an author index covering all three volumes. (MKR)