In this lecture, Cohen discussed the need for a sustainable energy source and why energy is the heart of the sustainability issue. He continues with a discussion about the technological challenges of energy including nuclear, solar and energy transmission. He talks about financing energy efficiency and renewable energy and the difference between the two. Finally, Cohen discusses the issue of organizational capacity as it relates to energy and the role of government and public policy in the energy business. Content in this video is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. http://creativecommons.org/licenses/by-nc-nd/3.0/