Terror attacks and natural disasters of the past decades have dramatically made governments, public health authorities, and communities aware of insufficiencies in crisis management practices. Information technology has the potential to advance these practices, but systems that support handling these courses of events still have low success rates. The authors set out to define a requirements engineering method suitable for the development of crisis management systems (CMS). The resulting method was formatively evaluated in a project aimed at defining functions for systems supporting international engagements in crisis situations. Each step in the method was documented by its objective, output, implementation, and the experiences gained from the case study. The most important features of the method are the Voice of the Customer Table for identification of user needs, Use Cases for determination of requirements from the needs, and scenarios and prototypes for validating the requirements with user representatives.