The rapid movement of information technologies into health care organizations has raised managerial concern regarding the capability of today's institutions to satisfactorily manage their introduction. Indeed, several health care institutions have consumed huge amounts of money and frustrated countless people in wasted information systems implementation efforts. Unfortunately, there are no easy answers as to why so many health informatics projects are not more successful. The aim of this study is to provide a deeper understanding of clinical information systems implementation. The research reported in this paper focuses on building a theory of the dynamic nature of the implementation process, that is, the how and why of what happened. The general approach taken was inspired by the work of Eisenhardt (1989) on building theories from case study research. We examined the implementation process, use and consequences of three distinct clinical information systems at a large tertiary care teaching hospital. A series of four research propositions reflecting the dynamic nature of the implementation process are offered as each of the three cases are analyzed. Findings add a number of new perspectives and empirical insights to the existing body of knowledge in the fields of IT implementation and medical informatics.