In this paper, a survey is undertaken of studies that examines the extent to which systematic patterns of behaviour in betting markets can generate above-average or even abnormal returns, the latter being most conveniently defined for these purposes as a profit. The paper concludes that although betting markets do tend to process efficiently the information available to them, there are clear opportunities to earn above-average returns. Moreover, there is significant evidence that some bettors are able to profit by withholding and subsequently utilising superior information.