With the development and penetration of business information systems, information systems outsourcing (IS Outsourcing) has attracted more and more interests from both managers and IT vendors. Meanwhile, there is an increasing number of theoretical research papers in academic journals. This paper reviews major theoretical research papers in this area and classifies them from the perspectives of research topics, research methods, journal categories, and theoretical foundations. Based on this review, we propose some directions for future research in IS outsourcing.