Many organisations are faced with complex decisions relating to the adoption and implementation of IS. These decisions are affected by the available information and other environmental and organisational influences. Evidence suggests that decision makers do not always use rational approaches to their decision making, yet anecdotal evidence indicates that very rational reasons appear in IS decision justifications. This paper will present a case study that examines the relationships between decision process, the factors that affect an IS decision and the factors that appear in the justification. The case study will focus on an ERP Data Warehouse implementation in a privately owned power utility.