Jonathan Barrett University of Oxford Any account of causality in the physical world should answer questions such as the following. If A is a cause of B, then what sort of thing are A and B? What does it mean to say that A is a direct cause of B? Do causal concepts involve, in an essential way, interventions by agents? Are causal relations directed in time? What, in the overall picture, is ontic (i.e., factual and independent of the agent), and what is epistemic (i.e., relative to an agent’s knowledge or beliefs)? I will give an account of causality in quantum theory that answers these questions, leading to a formalism for quantum causal modelling. The classical formalism for causal modelling can be recovered from this account, as a special case when quantum channels are all diagonal. Towards the end I will make some more speculative remarks about a possible new direction in the interpretation of quantum theory that is suggested by the work. The talk is based on (bits of): arXiv:1609.09487 arXiv:1906.10726 arXiv:2001.07774 arXiv:2002.12157 arXiv:2011.08120