This chapter analyses the four main theories of belief in some detail. These are the intellectualistic theory that belief is a cognitive act related to evidence that the thing believed is probably true, the dispositional theory that we recognize our own beliefs by observing how we react to things, the feeling theory that belief is a particular feeling that comes to us and is a signal to us that we believe or think to be true the thing under consideration, and eliminativist theories that belief does not exist, but is an illusion of our language and culture. The strengths and weaknesses of each theory are examined. The main weaknesses of the intellectualistic theory are the high frequency of irrational beliefs and beliefs the believer cannot justify with evidence, the speed and ease of belief, the inability to withhold judgement, and the largely involuntary nature of belief. The attempts that have been made to overcome these difficulties are considered. The main weaknesses of the feeling theory are that some people report that they are not aware of feelings of belief, that the theory makes use of subjective experience and introspection, that beliefs have duration and can continue beyond the brief time they are felt in consciousness, and the existence of what are called tacit or unconscious beliefs. The attempts that have been made to overcome these difficulties, including my own contribution, are considered. The balance of evidence seems to favour the feeling theory, and this theory is adopted.