Two informed estimates of the numbers of atheists and/or agnostics in the world, each published in the last fifteen years by reputable social scientists in major reference works, place the figure around or above half a billion people (Zuckerman 2007; Keysar and Navarro-Rivera 2013). Both rely, in very large measure, on what their authors readily admit to being reasonable guesswork. There is no shame whatsoever in this. Rigorous, nationally representative surveys don’t exist in large swathes of the world. In many places where they do, respondents may have reasonable anxieties about declaring, even on a seemingly confidential poll, a politically ‘wrong’ answer – in either direction. For example, China and Vietnam are the world’s first and fifteenth most populous countries, both are officially atheist, and neither is famous for freedoms of conscience or religion.