This paper describes a multi-disciplinary initiative to promote collaborative research in enactive artificial cognitive systems by developing the iCub : a open-systems 53 degree-of-freedom cognitive humanoid robot. At 94 cm tall, the iCub  is the same size as a three year-old child. It will be able to crawl on all fours and sit up, its hands will allow dexterous manipulation, and its head and eyes are fully articulated. It has visual, vestibular, auditory, and haptic sensory capabilities. As an open system, the design and documentation of all hardware and software is licensed under the Free Software Foundation GNU licences so that the system can be freely replicated and customized. We begin this paper by outlining the enactive approach to cognition, drawing out the implications for phylogenetic configuration, the necessity for ontogenetic development, and the importance of humanoid embodiment. This is followed by a short discussion of our motivation for adopting an open-systems approach. We proceed to describe the iCub’s  mechanical and electronic specifications, its software architecture, its cognitive architecture. We conclude by discussing the iCub  phylogeny, i.e. the robot’s intended innate abilities, and an scenario for ontogenesis based on human neo-natal development.