A central feature of debate and controversy within organisations has been the effectiveness or otherwise of cross-agency working. At the front end of service delivery this becomes a matter of what has become known as the ‘interoperability’ of agencies and professions as they work jointly in problem solving, particularly in emergency situations and incidents. This paper examines the specific issues of interoperability between police officers and ambulance staff engaging in street work. Based on interviews with 45 practitioners, it exposes the cultural dynamics of working together across these two organisations. Applying the conceptual framework of ‘communities of practice’ to this particular dynamic, it discusses the various dimensions of situated learning between police officers and ambulance staff which enable these two professions to operate in a relatively coherent fashion. It concludes that central to the front-end effectiveness of emergency response is the degree of ‘cultural interoperability’ which police officers and ambulance staff would appear to benefit from. Extending the communities of practice framework further, it focuses on two critical cultural features of interoperability: communication and exchange based behaviour.