Abstract. Open-ended exploration and learning in the real world is a major challenge of developmental robotics. Three properties of real-world sensorimotor spaces provide important conceptual and technical challenges: unlearnability, high-dimensionality and unboundedness. In this chapter, we argue that exploration in such spaces needs to be constrained and guided by several combined developmental mechanisms. While intrinsic motivation, i.e. curiosity-driven learning, is a key mechanism to address this challenge, it has to be complemented and integrated with other developmental constraints, in particular: sensorimotor primitives and embodiment, task space representations, maturational processes (i.e. adaptive changes of the embodied sensorimotor apparatus), and social guidance. We illustrate and discuss the potential of such an integration of developmental mechanisms in several robot learning experiments.A central aim of developmental robotics is to study the developmental mechanisms that allow life-long and open-ended learning of new skills and new knowledge in robots and animals (Asada et al., 2009;Lungarella et al., 2003;Weng et al., 2001). Strongly rooted in theories of human and animal development, embodied computational models are built both to explore how one could build more versatile and adaptive robots, as in the work presented in this chapter, and to explore new understandings of biological development (Oudeyer, 2010).Building machines capable of open-ended learning in the real world poses many difficult challenges. One of them is exploration, which is the central topic of this chapter. In order to be able to learn cumulatively an open-ended repertoire of skills, developmental robots, like animal babies and human infants, shall be equipped with task-independent mechanisms which push them to explore new activities and new situations. However, a major problem is that the continuous sensorimotor space of a typical robot, including its own body as well as all the potential interactions with the open-ended surrounding physical and social environment, is extremely large and high-dimensional. The set of skills that can potentially be learnt is actually infinite. Yet, within a life-time, only a small subset of them can be practiced and learnt. Thus the central question: how to explore and what to learn? And with this question comes an equally important question: What not to explore and what not to learn? Clearly, exploring randomly and/or trying to learn all possible sensorimotor skills will fail.