The term ‘self’ refers to a dynamic and evolving concept that is contrasted with our awareness of physical objects in the world and as such is the centre and focus of our internal experiences, as an awareness of ourselves as a centre of experience. This chapter deals with the philosophical accounts of John Locke, David Hume, Immanuel Kant and Derek Parfit. These varying accounts demonstrate that the concept of the self is not definitive but is situated in a shifting world of ideas. Karl Jaspers’ contribution was to set out formal characteristics of the self that developed out of encounters with patients and as such has clinical utility since it allows for a discussion of the abnormal phenomena that present to psychiatrists. Finally, our understanding of the neuroscience underpinning the self has advanced considerably to establish that there is no homunculus and the discovery of the default mode network confirms that at the very least the self is a distributed and dynamic network of structures that is most active when the mind is at rest and not focused on external tasks. It is involved in self-referential thinking, mind-wandering, autobiographical memory and social cognition. It is most active during daydreaming or letting the mind wander, when thinking about oneself or others, when recalling personal memories, imagining the future or engaging in moral reasoning and social understanding.