In this thesis I am going to explore the relationship between happiness and imprisonment. I will discuss three theories of happiness - hedonism, life satisfaction theories and emotional states theories. I will argue that the main problem of these theories is that they take happiness to consist only of psychological states. Because of this, I will turn my attention towards those theories that evaluate happiness in terms of how well life is going for the person who is living it. I will argue that my Aristotelian account is the most plausible way to understand the relationship between happiness and imprisonment. This is because it takes into account both the external circumstances and the psychological and emotional life of pnsoners. Through this thesis, I will show that my account of happiness in prison accomplishes three tasks: i) it solves the problems encountered by the other theories of happiness in the evaluation of prisoners' happiness, ii) it does not suffer from two of the main objections to the other objectivist theories of happiness, and iii) it can help us to investigate the happiness of prisoners empirically more accurately.