The concept of consciousness is omnipresent in the fields of neuroscience, quantum physics, philosophy and spirituality. In neuroscience, it represents the highest and least understandable component of brain function, unescapable but difficult to describe, its mechanism(s) remaining until today elusive. The dominant view in this field is that consciousness is an emergent product of the brain. In quantum physics, the relevance of the observer brings it into the center of discussions about interpretations of reality. It constitutes the hallmark of some models of quantum physics. In philosophy, it is also discussed at a fundamental level, sometimes refuted, other times placed in the center of the process of reality, as in the different philosophical idealistic approaches. In spirituality, it plays a central role in different eastern, monistic-idealistic, particularly hindu traditions. The aim of this chapter is, looking at a large scope going from the oldest spiritual to the most modern scientific approaches, to highlight the surprising and promising convergence of their data and concepts. It has been conceived to serve as a field overview for the different detailed reports presented in this volume.