"Green buildings" has emerged as a critical investment category at the nexus of energy security, environmental sustainability, and corporate social responsibility. Since 2000, venture capitalists have invested $4.06 billion in developers of equipment, systems, services, and materials that improve the energy efficiency of buildings and homes. Developers like Tridium, Encelium Technologies, and SAGE Electrochromics have advanced their technologies from seed-stage rounds to acquisitions by giants, and this early wave of acquisitions is poised to keep growing. However, opportunities for some current-generation technology and material developers are nearly gone, and exit prospects for their investors are bleak. Opportunities in integrated design, on-site generation, energy services, advanced building envelope, and low-carbon cement and concrete are all technology areas investors should pursue.