Journal articles and chapters on the cognitive science of religious belief often begin by highlighting the seeming ubiquity of supernatural beliefs (e.g. Pennycook et al. 2012). It is indeed rather striking that most of the world’s population share a similar sort of belief in a deity or greater power. According to Zuckerman (2007), approximately 90 per cent of the world’s population believe in a deity. In 2011, more than 92 per cent of Americans polled by Gallup answered yes when asked ‘Do you believe in God?’ – a number effectively unchanged since 1944 (96 per cent; Gallup 2011). These sorts of observations lead naturally to the conclusion that religious belief must be grounded in common and, perhaps, foundational cognitive mechanisms. We agree, though in this chapter we will instead emphasise religious doubt, a common experience among religious and non-religious alike (Hunsberger et al. 1993). In the same Gallup poll cited above, the number of respondents who answered ‘no’ when asked ‘Do you believe in God?’ increased from 1 per cent in 1944 to 7 per cent in 2011. Moreover, only 80 per cent identified as theists, and 12 per cent identified as deists when asked to distinguish between having belief in a personal God (theism) versus believing in a universal spirit/higher power (deism) in a 2010 poll (Gallup 2011). Finally, in a 2006 version of the same poll, 73 per cent indicated that they were convinced that God exists, with the remainder of the sample indicating some doubt or disbelief (Gallup 2011).