In unity with the technological evolution the conditions for cost-effective IT environments also changes. In this context, the architecture of software systems is changing and the business system design has to follow this development in order to be competitive on the IT market. Implementations of Service Oriented Architecture, abbreviated as SOA, have in many cases proven to be profitable investments to a modern architecture. This thesis explains in which ways SOA may turn out to be cost-effective for companies, and identifies critical success factors that are crucial within a system transition to SOA. The combination of a theoretical literature study, analysis of published business cases and empirical studies provided a result in which SOA-based solutions was cost-effective by reduced costs, time savings and faster product development. The study identifies five main critical success factors which are directly related to how cost-effective an implementation of SOA may be.