Sustainable ICT (SICT) can develop solutions that offer benefits both internally in IT and across the extended enterprise. However, because the field is new and evolving, few guidelines and best practices are available. There is a need to improve the SICT behaviours, practices and processes within organizations to deliver greater value from SICT. To address the issue, a consortium of leading organizations from industry, the nonprofits sector, and academia decided to develop a framework for systematically assessing and improving SICT capabilities. The SICT Capability Maturity Framework (SICT-CMF) gives organizations a vital tool to manage their sustainability capability. The framework provides a comprehensive value-based model for organizing, evaluating, planning, and managing SICT capabilities. Using the framework, organizations can assess the maturity of their SICT capability and systematically improve capabilities in a measurable way to meet the sustainability objectives including reducing environmental impacts and increasing profitability. The core of SICT-CMF is a maturity model for SICT which provides a management system with associated improvement roadmaps that guide senior IT and business management in selecting strategies to continuously improve, develop, and manage the sustainable IT capability. This chapter describes the SICT-CMF and the use of it to determine the maturity of sustainable IT capability within a number of leading organisations. The chapter highlights the challenges in managing SICT and motivates the benefit of maturity models. The development process for the SICT-CMF is discussed and the role of Design Science in the development cycle is explored. The application of the resulting model and its use to measure SICT maturity is discussed together with an analysis of the average results for organisations using the model. The chapter concludes with practical insights gained from the assessments.