The distribution of work, knowledge and responsibilities in the delivery of anaesthesia has attained particular significance recently as attempts to meet the demands of the European Working Times Directive intensify existing pressures to reorganise anaesthetic services. Using Lave and Wenger's (1991) notions of 'legitimate peripheral participation' in 'communities of practice' (and Wenger 1998) to analyse ethnographic data of anaesthetic practice we illustrate how work and knowledge are currently configured, and when knowledge may legitimately be taken as the basis for action. The ability to initiate action, to prescribe healthcare interventions, we suggest, is a critical element in the organisation of anaesthetic practices and therefore central to any attempts to reshape the delivery of anaesthetic services.