In 1993, Terry founded the Santa Monica BayKeeper and co-founded additional Waterkeeper programs in five California watersheds. He later served as the Executive Director of the Environment Now Foundation in Santa Monica, CA and co-founded the Frank G. Wells Environmental Law Clinic at the School of Law, University of California Los Angeles. In November 2003, Terry was appointed as the Secretary of the California Environmental Protection Agency by Governor Arnold Schwarzenegger and was later appointed Cabinet Secretary, the Chief Policy Advisor to the Governor. During his service in state government, Terry was the architect of many groundbreaking sustainability policies, including California's landmark Global Warming Solutions Act of 2006. In February 2007, Tamminen founded the non-profit organization Seventh Generation Advisors to help other states and world governments adopt clean energy and sustainability polices based on California's successes. That year he was also named the Cullman Senior Fellow for climate policy at The New America Foundation and was appointed as an Operating Advisor to Pegasus Capital Advisors, a private equity fund that provides capital to middle market companies across a wide variety of industries specializing in resource efficiency and sustainable technologies. In 2011 Terry was appointed as Strategic Advisor to the Founding Chair of the R20 Regions of Climate Action, created in 2010 by Governor Arnold Schwarzenegger and other sub-national leaders. As the Founding Chair's Strategic Advisor, Terry advises the R20 on policy and helping with the design and implementation of climate resilient economic development projects. An accomplished author, Terry's book, Lives Per Gallon: The True Cost of Our Oil Addiction (Island Press), is a timely examination of our dependence on oil and a strategy to evolve to more sustainable energy sources. His book, Cracking the Carbon Code: The Keys to Sustainable Profits in the New Economy (Palgrave) shows how to find the low carbon products and services that save money, get ahead of regulations, and preserve resources for generations to come. Terry was named Vanity Fair's May 2007 Environmental Hero and in 2008 The Guardian ranked Terry No. 1 in its "Top 50 People Who Can Save the Planet." In 2011, he was named one of six finalists for the 2011 Zayed Future Energy Prize.