Muscles and tendons are the main form of joint actuation in nature. The biological muscle provides a very high power to weight ratio, a high velocity with big torque and an inherent controllable spring-damper system. In co-operation with the company FESTO the six-legged walking machine AirBug has been developed, using FESTOs fluidic muscle. This pneumatic muscle, based on the McKibben muscle, provides a good weight to power ratio (not considering the external compressor) and mimics the force-length correlation of its biological paragon. Each joint has two antagonistic muscles as actuators, allowing to control the position, the torque and the stiffness of each joint. Since the stiffness of the joint is regulated by using the characteristics of the muscle, no special close-loop control as for example active compliance is needed, which means that no extra computing time is used and that it works without power supply. AirBug had a successful maiden presentation at Hannover Fair 2001/2002. Current work includes the mechanical optimisation of the robot, the redesign of the central body, and the enhancement of the low-level control algorithms, there considering the insights of the research at neuro-biological institutes.