The way things are made and how much energy we use now is fueling a booming green-technology (green-tech) market that is all about new ideas and better environmental performance. It's hard to figure out their research and development (R&D) and innovation tracks because most green-tech companies are innovative start-ups or small and medium-sized businesses (SMEs). These companies have a lot of intangible assets and aren't sure what the future holds for technology. Greentech companies also tend to cluster together, and around the world, this is becoming more and more recognized as a way to encourage new production and research and development activities as well as a shift to sustainable energy. This essay looks into green-tech companies in San Francisco, New York, and London To find out what they specialize in, how their technologies and/or markets work together, and what new groups and clusters are forming. We suggest a network analysis using metadata on the technological a...