Under the Kyoto Protocol, countries can meet treaty obligations by investing in projects that reduce or sequester greenhouse gases elsewhere. Prior to ratification, treaty participants agreed to launch country-based pilot projects, referred to collectively as Activities Implemented Jointly (AIJ), to test novel aspects of the project-related provisions. Relying on a ten-year history of projects, we investigate the determinants of AIJ investment. Our findings suggest that review-agency preferences related to national political objectives and possibly deeper cultural ties influenced project selection and limited the number of AIJ projects. Bilateral ties also appear to have affected investment decisions directly, possibly because of related transaction costs. The results suggest an investment process different from the assumptions that underlie well-known estimates of cost-savings related to the Protocol's flexibility mechanisms. We conclude that if approaches developed under the AIJ programs to approve projects are retained, the scale of investment under Kyoto's flexibility provisions and their cost-savings will be less than what is generally anticipated and the pattern of investment less driven by abatement costs.