This paper investigates the evolution of the multitude of alternative building certification/ assessment rating systems around the world. In addition, the paper compares best practices, with a particular focus on the two most commonly used and/or modified environmental assessment systems ñ LEED (Leadership in Environmental and Energy Design) and BREEAM (Building Research Establishment Environmental Assessment Method). In order for these certification/assessment rating systems to continue to push for innovation, it will be important that they begin to converge and speak the same language, so this paper will explore the different philosophies and business models from which they have evolved. Similarities will be identified, topics of significant difference will be highlighted, and strengths and weaknesses of each system currently being applied will be described. Issues that remain to be tackled by the rating systems ñ e.g. such as a need to move beyond checklists to better performance indicators that measure performance more holistically ñ are identified for further research.