Response to large-scale emergencies is a cooperative process that requires the active and coordinated participation of a variety of functionally independent agencies operating in adjacent regions. In practice, this essential cooperation is sometimes not attained or is reduced due to poor information sharing, non-fluent communication flows, and lack of coordination. We report an empirical study of IT-mediated cooperation among Spanish response agencies and we describe the challenges of adoption, information sharing, communication flows, and coordination among agencies that do not share a unity of command. We analyze three strategies aimed at supporting acceptance and surmounting political, organizational and personal distrust or skepticism: participatory design, advanced collaborative tools inducing cognitive absorption, and end-user communities of practice.