We are all familiar with self deception, though we may not know it by that name. Most of us, at one time or another, have encountered gamblers, alcoholics or addicts who deny the gravity of their compulsions despite evidence to the contrary. We know of the lover who covers up a partners cheating behaviour in order to allay a break up; a terminally ill patient who refuses to accept they are going to die despite contrary indications, and the all too mediocre student who is convinced he will get an A grade despite failing results. Self deception is an all too ubiquitous piece of human theatre. But do we really understand what this behaviour involves and why people do it? Is self deception a rational way to behave? Indeed, is it even a coherent term in the first place? This book sets out to answer these and other questions. Self deception appears at first to be a conceptually incoherent term which generates some interesting paradoxes. These paradoxes can be appreciated by considering what it means to deceive another person. In deceiving another, there is firstly a discrepancy in the beliefs that the 2 parties (deceiver and deceived) hold. The deceiver secondly intends to mislead another person who is unaware that he is being deceived. It now appears that there could be no deception of oneself for 2 reasons. If we self deceive, we must be simultaneously holding 2 contradictory beliefs where one is motivationally sustained by the other. Our ordinary notions of belief seem to go against this idea. Secondly, in deceiving ourselves, we must act with a strategy in which we knowingly hide something from ourselves without our knowing what we are getting up to, except that this seems to be necessary to the process. A number of attempts to deal with these paradoxes are discussed, some of which rely on a radical redescription of the behaviour associated with self deception. One theory tries to get round this problem by postulating that in every agent, there are 2 centres of agency, one of which is responsible for the deception of the other. The deceiving agent like entity has one belief and the deceived agent like entity has another, while the latter is ignorant of the deception taking place. But this is criticized as a counter intuitive approach which simply creates problems of a different kind. In the next 2 chapters, various methods are described by which people deceive themselves and these are not shown to be solely intentional. Some recent work in cognitive psychology is brought to bear on this issue including experiments on human motivation, perception and irrationality. In the next chapter, a mental model is offered which is used to explain self deception but which dispels any idea of paradox. This model uses a metaphorical notion of mental partitions and unconscious intentions to explain how it is that we can simultaneously entertain contrary beliefs and strategically deceive ourselves. This model of self deception is applied to Freudian case studies to show why classical psychoanalysis is not really a theory of standard self deception. To do this, two of Freuds better known case studies are discussed, including the famous case of the Ratman. The final chapter examines whether self deception can be considered rational and the conclusion drawn is that the answer is by no means as straightforward as first appears.