**1. Introduction**

The purpose of this chapter is both to review the current state of the art in robotics and to identify some of the challenges that the field has yet to face. This is done and illustrated by following an imaginary roboticist, Rob, who is currently designing a new humanoid robot from scratch. Rob's ultimate vision is that this robot will be humanoid in the sense that it possesses the abilities of a human being. Therefore, his initial aim is to identify relevant work as well as areas in which innovations are still needed.

Research in robotics has come a long way in the last few decades, whether one considers humanoids specifically or just any type of architecture. The world is increasingly moving away from being confined to industrial robots with precisely programmed movement plans and is beginning to include adaptive robots that can robustly operate in a variety of scenarios as well as robots that show increasing levels of cognitive abilities and intelligence. We have witnessed an increasing collaboration between research areas that, previously, had very little in common. Nowadays, it is not difficult to find research groups uniting neuroscientists, engineers, psychologists, linguists, even philosophers and musicians, all coming together to study the human body as well as the human mind. There is thus plenty of previous work that Rob can build upon when designing his robot. At the same time, it is clear that the field is still a long way from creating truly human-like machines and that there are thus significant challenges to overcome.

In this chapter, we first provide a brief history of humanoid robotics research since it sets the background to Rob's work. We then present the state of the art in the different components of a robot, hardware as well as software, discussed in contrast with Rob's requirements and highlighting particular areas in which further research is needed before Rob's robot can become reality.
