LEARNING techniques are increasingly being used in today's complex robotic systems. Robots are expected to deal with a large variety of tasks using their high-dimensional and complex bodies, to manipulate objects and also, to interact with humans in an intuitive and friendly way. In this new setting, not all relevant information is available at design time, and robots should typically be able to learn, through self-ex- perimentation or through human–robot interaction, how to tune their innate perceptual-motor skills or to learn, cumulatively, novel skills that were not preprogrammed initially. In a word, robots need to have the capacity to develop in an open-ended manner and in an open-ended environment, in a way that is analogous to human development which combines genetic and epigenetic factors. This challenge is at the center of the developmental robotics field. Among the various technical challenges that are raised by these issues, exploration is paramount. Self-experimentation and learning by interacting with the physical and social world is essential to acquire new knowledge and skills.