We describe the concept of complementarity and argue that it is a useful concept for consciousness and other studies at the interface of conscious phenomena and physical reality. After outlining the history and source of the concept within psychology, we describe its place as a working hypothesis for the mind-brain problem. We then point out that generalized quantum non-locality could be of importance even for macroscopic objects. If this is so, complementarity would be the key-concept to understand EPR-like correlated systems.