A hidden repertoire is a functional configuration in the brain that supports behaviour but is seldom used. As a complex system, the brain can show a broad range of configurations for the same function. This “many-to-one” property imparts our brain with resilience during normal operations but also in the face of adverse events, such as damage or disease. I will cover the evidence for these repertoires and cover strategies for investigation, and the implication for the I will also relate the existence of such repertoires to variations in the qualia of our experience.