In today's business world, information systems (IS) are often acquired from an external vendor rather than being developed in-house. Although the number of studies related to the success of IS acquisitions has increased, there is limited understanding of the relationship between acquisition project success, the final IS success, and their role in defining whether the acquisition endeavor was ultimately successful. For instance, in public sector organizations, there is a tendency for the acquisition project to be conducted outside the acquiring unit. This means that success can be evaluated at multiple levels in the organization, and the different levels might not have identical aspirations related to the acquisition. This can cause organizational issues, especially when the evaluation of success is left in the hands of only one of these parties. In this paper, we study the facets of IS acquisition success by presenting differing aspects that are used in defining IS acquisition success, pointing out a contradiction between the formally measured success and the perceived success. As a result, we propose an IS acquisition success model. The study is conducted as a single case study of a public sector organization in Finland.