John Heil (Washington University in St. Louis) gives a talk for the Metaphysics of Relations Conference, held on 3rd-5th October 2012 in University of London. On the received view of causation, causal relations are a distinctive species of external relation. This paper explores the implications of adopting a conception of causation according to which causal relations are understood as manifestings of reciprocal powers. On such a conception, causation would most naturally be seen as a kind of internal relation, a relation founded on non-relational features of its relata. The consequences of such a view for familiar conceptions of natural necessity are assessed.