In the rapidly growing economies of Southeast Asia, energy consumption and energy costs in buildings continue to increase. Over the past decade, energy consumption from the commercial building sector in Thailand has increased at an average of 4% per annum and currently represents over 30% of total electricity consumption, second only to the industrial sector. Buildings that exist today will continue to represent most of both energy and greenhouse gas (GHG) emissions from the built environment, with newly constructed buildings representing only a small additional portion. This paper analyzes the environmental, technical, and financial characteristics of energy efficiency retrofit activities in commercial buildings in Thailand through detailed case studies of forty-two projects undertaken over the past 8 years. Our findings suggest that retrofits provide significant opportunities to reduce energy use, energy costs, and GHG emissions while also validating the economic feasibility of investments into such retrofit activities. Through this detailed analysis of past retrofit projects in Thailand, we found that the marginal abatement costs (MAC) relating to the key energy conservation measures (ECM) implemented within these retrofit projects all have negative costs. However, although these findings demonstrate positive economics and should be sufficient to instigate widespread adoption, in reality, this is not taking place. It is evident that greater public policy and leadership are needed to stimulate growth in the building retrofit sector to take advantage of the opportunities and benefits that building retrofits offer.