Buildings are the largest contributor to greenhouse emissions, and three-quarters of U.S. energy goes to building operations. Yet, there is no way to accurately predict building performance. There is a need for simple tools and protocols to provide meaningful and actionable feedback on building performance to designers, owners and occupants. BLDG 2.0 seeks to fill the void between design intent and building performance. Built upon principles of mass collaboration and collective intelligence, BLDG 2.0 is an open-source interface to building performance databases, a collaborative community of experts, and an online marketplace for ideas emphasizing building energy performance and open innovation.