This dissertation looks at some of the most important theories of humour and laughter, and aims to consider how successful or otherwise those theories have been in explaining these complex phenomena. After a general introduction in Chapter One, each of Chapters Two to Four offers an analysis of one of the three main theoretical traditions: what have been labelled the incongruity, superiority and release theories. Key figures in these traditions are Schopenhauer (incongruity), Hobbes (superiority) and Freud (release). My analyses are lengthy, constituting the bulk of the dissertation, because of the need to consider each theory in more detail than has been the case in previous, often very superficial, reviews. Each of them is ultimately rej...