Expectations for high performance green buildings have been evolving over the last four decades. Green certification systems define, recognize, and demonstrate leadership in addressing building problems related to people and the environment. These systems are premised on a theory of change where making the distribution in building performance visible provides opportunities for competitive differentiation that motivates and rewards action to create better spaces, buildings, and places. To date, there are more than 200 different green building certification programs around the globe, with estimates of at least 1 million certified projects.