This proceedings of the annual conference of the International Group for the Psychology of Mathematics Education (PME) includes the following research papers: "A Model of Understanding Two-Digit Numeration and Computation" (H. Murray & A. Olivier); "The Computer Produces a Special Graphic Situation of Learning the Change of Coordinate System" (S. Nadot); "Epistemological Analysis of Early Multiplication" (N. Nantais & N. Herscovics); "Are the Van Hiele Levels Applicable to Transformation Geometry?" (L. Nasser); "Intuitive and Formal Learning of Ratio Concepts" (P. Nesher & M. Sukenik); "Early Conceptions of Subtraction" (D. Neuman); "Computational, Estimation Performance and Strategies Used by Select Fifth and Eighth Grade Japanese Students" (N. Nohda, J. Ishida, K. Shimizu, S. Yoshikawa, R.E. Reys, & B.J. Reys); "Associations Among High School Students' Interactions with Logo and Mathematical Thinking" (J. Olive); "Graphic Constructions with Computer to Learn 3D Reference Systems" (I. Osta); "Applied Problem Solving in Intuitive Geometry" (J.P. Pace); "L'incidence de l'Environment sur la Perception et la Representation d'Objets Geometriques" (R. Pallascio, L. Talbot, R. Allaire, & P. Mongeau); "Angles et Pixels - Quelle Synergie a 9 Ans?" (C. Parmentier); "Interaction by Open Discussion and 'Scientific Debate' in a Class of 12-Years Old Pupils" (T. Patronis); "Formal and Informal Sources of Mental Models for Negative Numbers" (I. Peled, S. Mukhopadhyay, & L.B. Resnick); "Inverse Procedures: The Influence of a Didactic Proposal on Pupils' Strategies" (A. Pesci);"Through the Recursive Eye: Mathematical Understanding as a Dynamic Phenomenon" (S. Pirie & T. Kieren); "Cognitive Aspects of the Learning of Mathematics in a Multicultural School" (N. Presmeg & A. Frank); "Qualitative and Quantitative Predictions as Determinants of System Control" (M. Reiss); "Transfer between Function Representations: A Computational Model" (B. Schwarz & T. Dreyfus); "Transition from Operational to Structural Conception: The Notion of Function Revisited" (A. Sfard); "Supercalculators and Research on Learning" (R. Shumway); "How and When Attitudes Towards Mathematics and Infinity Become Constituted into Obstacles in Students?" (A. Sierpinska & M. Viwegier); "Learning Y-Intercept: Assembling the Pieces of an 'Atomic' Concept" (J. Smith, A. Arcavi, & A.H. Schoenfeld);"Computers, Video, Both or Neither: Which is Better for Teaching Geometry?" (N. Snir, Z. Mevarech, & N. Movshovitz-Hadar); "Vocational Mathematics Teachers' Cognition of Mathematical and Vocational Knowledge" (R. Strasser & R. Bromme); "Training Elementary Teachers in Problem Solving Strategies: Impact on Their Students' Performance" (J.K. Stonewater); "Developing Algebraic Understanding: The Potential of a Computer Based Environment" (R. Sutherland); "Verbal Evidence for Versatile Understanding of Variables in a Computer Environment" (M. Thomas & D. Tall); "Conceptual Adjustments in Progressing From Real to Complex Numbers" (D. Tirosh & N. Almog); "Does the Semantic Structure of Word Problems Affect Second Graders' Eye-Movements?" (L. Vershaffel, E. de Corte, & A. Pauwels); "The Lesson - A Preconceptional Stage" (S. Vinner); "An Analysis of the Emotional Acts of Young Children While Learning Mathematics" (E. Yackel, P. Cobb, & T. Wood); "The Use of Graphs as Visual Interactive Feedback While Carrying Out Algebraic Transformations" (M. Yerushalmy); "Images of Geometrical Transformations: From Euclid to the Turtle and Back" (R. Zazkis & U. Leron); and "A Knowledge-Base of Student Reasoning about Characteristics of Functions" (N. Zehavi & B. Schwarz). Includes a listing of author addresses. (MKR)