Although many researchers and practitioners have discussed different aspects of outsourcing in the past, there have been only a handful of papers that grapple these complex issues from a broad perspective. The main purpose of this study is to lay an integrative groundwork for the understanding of outsourcing, including its key research areas, its evolution, its theoretical models, and its future research trend. From our review of the past studies, we identify the key research areas and their evolution that help to provide a deeper understanding on the outsourcing trend. Essentially, we propose that the previous research can be represented in two stages: the first stage based on clients' view, hierarchical relationship, and win-lose strategy; the second stage based on both the clients and the service providers' views, equal relationship, and win-win strategy. From this classification, we introduce an integrative perspective that focuses on both stages as a way to understand the emergence of partnership-based outsourcing. The critical outsourcing issues and the integrative theoretical perspective presented in this study may provide new insights in the direction and focus of future outsourcing research.