Water is an important physical and conceptual resource in religion, which should be unsurprising, for only air is more critical to life. Water may be perceived as sacred or defiled and, whether pristine or polluted, the places where it is accessed are often considered sacred. Pilgrimages to such places, and practices undertaken there, are often religiously meaningful and sometimes obligatory. Water is a powerful substance that can and has been used in different ways by people trying to make meaning of their experiences (Rudhardt 2005). It can be a source of wisdom or mysterious, cathartic power; or conversely, a force in opposition to divine purposes and in need of subjugation (ibid.; see also Tvedt and Oestigaard 2006). Yet despite the often central role of water in religious life, there has been little scholarly attention to the sea in religious perception and practice, even though today over half of the world's population lives within 200 kilometres of the sea and two-thirds within 400 kilometres. This volume represents an effort to rectify this inattention as it asks: what does the sea, and water more generally, have to do with spirituality? The short answer is that sea-spirituality is an important, global, form of nature religion; specifically, one that I consider to be a form of ‘aquatic nature religion’.