ThesearetheproceedingsoftheRoboCup2004Symposium, heldattheInstituto Superior T ecnico, in Lisbon, Portugal in conjunction with the RoboCup c- petition. The papers presented here document the many innovations in robotics that result from RoboCup. A problem in any branch of science or engineering is how to devise tests that can provide objective comparisons between alt- native methods. In recent years, competitive engineering challenges have been established to motivate researchers to tackle di?cult problems while providing a framework for the comparison of results. RoboCup was one of the ?rst...