Stages of growth models have been used widely in both organizational research and information technology management research. According to King and Teo (1997), these models describe a wide variety of phenomena – the organizational life cycle, product life cycle, biological growth, stages of growth in information systems, growth model for integration between business planning and information systems planning, electronic commerce evolution, stages of knowledge management technology, and a number of other interesting developments in time perspectives. These models assume that predictable patterns (conceptualized in terms of stages or levels) exist in the growth of organizations and organizational parts, the sales levels of products, and the growth of living organisms. These stages are (1) sequential in nature, (2) occur as a hierarchical progression that is not easily reversed, and (3) evolve a broad range of organizational activities and structures. This chapter starts with an introduction to stages of growth models. In the following sections we present the three-stage model for the evolution of IT outsourcing relationships (Gottschalk & Solli-Sæther, 2006). The three stages are labelled cost stage, resource stage, and partnership stage respectively. Theory-based benchmark variables for measuring maturity in IT outsourcing relationships are presented, followed by the stage hypothesis and a description of how benchmark variables are used to indicate characteristics at each stage of growth. Finally in this chapter, we present results from an exploratory study testing the stage model. The purpose of this chapter is to develop a framework for improved understanding of the current situation in an IT outsourcing relationship in terms of a specific stage, to develop strategies for moving to a higher stage in the future, and to learn from earlier stage experience.