Information Systems Development Methodology (ISDM) tailoring is often portrayed as a simple linear process. In this study, the use of an ISDM on a complex, multi-million dollar commercial project is examined. It reveals that ISDM tailoring should be viewed as a complex series of tailoring steps, some of which occur in a proactive (or “contingent”) way in response to known or planned project conditions, whilst others are more reactive in nature and represent improvised responses to project conditions which emerge.