This document contains the first volume of the proceedings of the 26th Annual Conference of the International Group for the Psychology of Mathematics Education. Conference presentations are centered around the theme "Learning from Learners". In total, 290 presentations were given ranging from the psychology of mathematics in the very early years to discussions on advanced mathematical concepts. This volume features nine plenary papers, papers from four groups of research forums, discussion groups, working sessions, and short oral communications. Plenary papers include: (1) "Little Children, Big Mathematics: Learning and Teaching in the Pre-School" (Herbert P. Ginsburg); (2) "Researching Primary Numeracy" (Margaret Brown); (3) "How Students Structure Their Own Investigations and Educate Us: What We've Learned from a 14 Year Study" (Carolyn A. Maher); (4) "Mathematical Epistemologies at Work" (Richard Noss); (5) "Taking the Modeling Perspective Seriously at the Elementary School Level: Promises and Pitfalls" (Lieven Verschaffel); (6) "Learning from Learners" (Joao Filipe Matos); (7) "Episode 1: How Karin Disturbed Her Teacher's Line of Reasoning" (Joop Van Dormolen); (8) "Episode 2: Marco and Anna--Each Following Their Own Path" (Rosetta Zan); and (9) "Episode 3: Calculators--The First Day" (Susie Groves). (KHR)