Software-as-a-Service (SaaS) is emerging as a viable outsourcing option for clients interested in paying for the right to access through the network a standardized set of business software functions. SaaS model largely replaced the Application Service Providers (ASPs)-based model, by creating an architecture that that provides no mechanisms for customizing the software on the vendor side; all customization is done on the client side through standardized interfaces. The fact that vendors are not making any client-specific investments makes this outsourcing model quite intriguing. In this paper we investigate client’s side determinants of adopting the SaaS model. We draw on economic, strategic management, and IS theories to develop a theoretical framework. In it, we develop a more elaborate view of uncertainty as some types uncertainty increase the propensity to adopt SaaS, while other types do the opposite. Finally, we integrate the role of the internal enterprise IT architecture into our model.