When men and women in early medieval England thought about the world around them, they did so in ways that often strike us as strange. In their surviving writings, we are confronted continually with unfamiliar ideas – about the creatures and beings which populated the world, about the forces and phenomena which shaped it, and about the ways in which human beings might enact change upon it through ritual, magic, and prayer. Although unfamiliar, these ideas give us important indications of how early medieval English thinkers characterized and categorized their surroundings and their experiences. Of substantial interest to many of them was the question of how they might distinguish correctly between what was 'natural' in the world, and what was not. This Element examines what that distinction meant to the inhabitants of early medieval England, and under what circumstances they felt compelled to explore it.