The Proceedings of PME-XVIII have been published in four separate volumes because of the large number of individual conference papers reported. Volume I contains brief reports for 11 Working Groups and 8 Discussion Groups, 55 "Short Oral Communications," 28 Posters, 5 Plenary Panel reports, and 4 Plenary Session reports. Volume II contains 50 Research Reports covering authors with last names starting with A-G. Volume III contains 52 Research Reports covering authors with last names starting with G-O. Volume IV contains 54 Research Reports covering authors with last names starting with P-Z. In summary, the four volumes contain 156 full-scale Research Reports, 4 full-scale Plenary Session Reports, and 57 briefer items. Conference subject content can be conveyed by a listing of the Plenary Panels and Plenary Session Reports. Plenary Panels: "The History of Mathematics and the Learning of Mathematics: Psychological Issues (Paul Ernest); "Relations Between History and Didactics of Mathematics" (Lucia Grugnetti); "The Case of Pre-Symbolic Algebra and the Operation of the Unknown" (Teresa Rojano); "What History of Mathematics Has to Offer to Psychology of Mathematical Thinking" (Anna Sfard); "Practical Uses of Mathematics in the Past: A Historical Approach to the Learning of Mathematics" (Eduardo Veloso). Plenary Session Reports: "The Historical Dimension of Mathematical Understanding--Objectifying the Subjective" (Hans Niels Jahnke); "A Functional Approach to the Introduction of Algebra: Some Pros and Cons" (Carolyn Kieran); "Researching from the Inside in Mathematics Education: Locating an I-You Relationship" (John Mason); "Mathematics Teachers' Professional Knowledge" (Joao Pedro da Ponte). (MKR)