Recent research on the social and cultural aspects of systems development work has focused on the work of professional software and systems designers. A complementary approach is to look at the work of end users as systems developers, whose informal systems design work is frequently ignored or undervalued in organizations and by IS researchers. This case study, of an application to facilitate dispatch work in a large organization, describes a history of collaboration and conflict between IS professionals and end users as systems designers. Application development was initiated by end users, the initial programming was carried out by IS professionals in collaboration with end users, and the subsequent implementation and enhancement of the application was shared, and passed back and forth between end users and the organization's IS department over a period of several years. We take a Social Construction of Technology approach to describing this history, examining the mixture of cooperation and conflict between the Dispatch and IS departments in terms of the differing interpretations of the application by the social groups involved in its history. A constructivist approach to studying systems design allows us to recognize the unique expertise end users bring to systems development work, and provides a useful means for describing the political aspects of systems design and implementation over an extended time period.