Despite outsourcing is at the core of many for decisions on IT investments, the extant literature still does not provide a clear understanding of the overall phenomenon. This chapter answers two main questions, relevant to researchers and practitioners: 1.What are the main findings so far in outsourcing literature? 2.What do we still need to learn? Through a comprehensive review of the literature, we offer systematization of the existent body of knowledge on outsourcing, its implications on firms’ boundaries, and the theoretical challenges. The MIS perspective appears to be very present, both by considering technology as part of the external environment, and by exploring IS and IT as areas for important sourcing decision. In conclusion, implications for managers are drawn.