This chapter introduces the ERP software acquisition process based on a rational or normative decision-making approach embedded within the wider ERP system lifecycle. It presents five hypotheses closely related to practical problems during ERP system acquisition, which were derived from a review of recent academic literature and suggestions from students, practitioners and researchers. Based on perceptions of an empirical survey of Austrian organizations, the hypotheses and every stage of the proposed acquisition process model were investigated. Special consideration was given to the differences between small to medium and large organizations. It was assumed that these differ in several phases of the acquisition process. As most ERP system suppliers are today striving to penetrate the market segment of small to medium enterprises, with the market for large organizations mostly saturated, this point warrants particular interest.