This book constitutes the proceedings of the 26th RoboCup International Symposium which was held in Bordeaux, France, during July 4-10, 2023. The 25 regular papers included in these proceedings were carefully reviewed and selected from 47 submissions; the volume also includes 11 RoboCup Champions Papers. In addition to presenting the proceedings of the RoboCup 2023 Symposium, the book highlights the approaches of champion teams from the competitions. Due to the complex research challenges set by the RoboCup initiative, the RoboCup International Symposium offers a unique perspective for exploring scientific and engineering principles underlying advanced robotic and AI systems.