This chapter notes and explains the increasing use of outsourcing and service level agreements (SLAs); proposes and describes an outsourcing methodology emphasising the role of SLAs; stresses SLAs’ importance to insourcing and outsourcing relationships; proposes a taxonomy of service attributes, and recommends a hierarchical methodology for constructing SLAs. Evidence from interviews and examination of extant SLAs suggests that well-designed SLAs contribute to fruitful relationships between business partners. The proposed methodology and taxonomy will simplify and shorten the time-consuming tasks of writing and negotiating SLAs that are complete, consistent and satisfy business objectives. SLAs have not received academic attention proportionate to their commercial importance. Recommendations to practitioners and for further research are given, In particular, research ascertaining whether SLAs are used effectively and seeking better expression of business requirements in an SLA is appropriate.