The purpose of this document is to fully describe the Smart Grid Maturity Model (SGMM). The document describes the levels and domains that compose the SGMM and provides introductory material to aid in understanding the purpose and use of the model. The SGMM is a management tool under the stewardship of the Software Engineering Institute at Carnegie Mellon University. The model was originally developed by electric power utilities for use by electric power utilities. The model provides a framework for understanding the current state of smart grid deployment and capability within an electric utility and provides a context for establishing future strategies and work plans as they pertain to smart grid implementations. It is composed of eight model domains that each contain six defined levels of maturity, ranging from Level 0 (lowest) to Level 5.