Service-Oriented Architecture (SOA) is a way of designing, developing, deploying, and managing enterprise systems where business needs and technical solutions are closely aligned. SOA offers a number of potential benefits, such as cost-efficiency and agility. To exploit the benefits that SOA offers, several organizations are adopting a services model for leveraging their existing legacy systems. Migration to SOA can give new life to the existing legacy, but if not done correctly the migration can also lead to failure. There are several factors for this, such as technology selection, migration approach, type of legacy system, and SOA governance. One way to learn how to achieve success and avoid failure is through a thorough analysis of existing work in this field. This paper reports on a study that analyzed existing SOA migration projects to learn from them the factors that influence the success or failure of their efforts. A mechanism called the Evolution Process Framework for SOA was used to structure the analysis. Three SOA migration case studies and one experience report were analyzed. Lessons learned from each study are summarized, with crosscutting issues distilled from across all four studies presented. One of the most important lessons learned is the significance of well-defined policies and procedures for defining, publishing, and maintaining services.