Abstract. This paper traces four years of evolution of the UNSW team in the RoboCup Sony legged robot league. The lessons learned in the creation of a competitive team are instructive for a wide range of applications of robotics. We describe the development of vision and localisation procedures for robot soccer, as well as innovations in locomotion and the design of game play strategies. Since all teams in the competition are required to use identical hardware, the key factor to success in this league is the creativity of the software designers in programming the robots to perform skills that the robots were not originally intended to do and to perform them in a highly dynamic and non-deterministic environment.