The relationship between Marcus’ views of natural philosophy and his ethical commitments has long been a vexed issue. This chapter aims first to clarify what Marcus’ own views on physics were, relying only on the contents of the Meditations, and only then to ask how these views relate to those of earlier Stoics and to consider whether Marcus’ position was a good one for him to hold. It becomes clear that Marcus regards nature, which is for him identical with god, as directly setting some important norms for human beings, most importantly because of the thorough integration of humans into the providential and teleological order of the cosmos. Marcus’ understanding of the natural world includes his conception of human nature as naturally social, which entails other important norms for human behaviour. Humans are, for Marcus, integrated ‘vertically’ with the cosmic order and ‘horizontally’ with other human beings; these integrations structure a great deal of Marcus’ ethical theory. But natural philosophy is far from being the only source of norms for Marcus; reflection on his relationships with other people and on the workings of his own mind also have impact and, as I suggest, may even lead him to views which conflict with the materialist determinism of most earlier Stoics.