The distinction between doing and allowing appears to have moral significance, but the very nature of the distinction is as yet unclear. Philippa Foot's ‘pre-existing threats’ account of the doing/allowing distinction is highly influential. According to the best version of Foot's account an agent brings about an outcome if and only if his behaviour is part of the sequence leading to that outcome. When understood in this way, Foot's account escapes objections by Warren Quinn and Jonathan Bennett. However, more analysis is required to show what makes a relevant condition part of a sequence. Foot's account is promising, but incomplete.