The belief revision approach, as has been indicated, involves forming an initial belief and then updating or revising this belief according to new pieces of confirming and disconfirming evidence. Auditors' formation of the initial belief and the weight assigned by them to pieces of evidence will depend on a number of factors. These factors have not actually been agreed upon, and no specific list of them has been suggested. However, a review of the auditing literature, indicates that factors affecting auditors' formation of the initial belief and their attitudes toward confirming and disconfirming evidence can be classified into seven factors. These factors are belief formation, confirmation bias, diagnostic content of evidence, expertise, professional scepticism, motivational factors, and cognitive factors. The aim of this chapter is to discuss the main findings of previous auditing studies concerning the effect of these factors.