The management of large-scale civil emergencies is a complex undertaking. Possible emergency scenarios include terrorist attacks; serious accidents; environmental emergencies, such as flooding; and the outbreak of animal and human diseases. A responsibility model for civil emergency planning refers to the specification of responsibilities involved in handling some civil emergency, the agents or agencies that have been assigned specific responsibilities and the relations between agencies, responsibilities, and resources. In the model of responsibility presented in this paper, an "agent" may become the holder of a "responsibility" through an act of "assignment" by another agent or through organizational custom and practices. Agents may be organizations or individuals; for example, police are assigned as agents for the responsibility of "maintaining law and order." Some responsibilities will be discharged by an "agent" that consists of representatives of multiple organizations; for example, the responsibility of command and control may be performed by a body composed of representatives of the police, ambulance service, and fire and rescue service, so as to ensure coordination and efficiency in how the distinctive responsibilities of each of these agencies meshes with the responsibilities of the other agencies. This paper outlines the particular framework for contingency planning used in the United Kingdom and introduces the concept of responsibility models as a means of depicting the key features of contingency plans. A case study of a flooding emergency is used to illustrate the proposed approach to responsibility modeling. 13 figures and 37 references