Sustainable public procurement (SPP) helps government stimulate market demand for green products and reduce greenhouse gasses across the supply chain. To address greenhouse gas (GHG) emissions impacts associated with public procurement, the Japanese and U.S. federal governments, and more than 475 Japanese and 500 U.S. local governments, have implemented sustainable public procurement (SPP) policies. In 2001, by directive, the Japan Ministry of Environment (MOE) developed an SPP and green product criteria spanning over 250 products. However, implementation efforts are inconsistent at the local level, with some cities using GHG information in their purchasing decisions to a greater extent than others. By contrast, in the U.S., there is no federal policy requiring local governments to implement SPPs, which is why most local governments do not have them. Of those that do, the lack of federal SPP directive means that local governments have significant flexibility in how their SPPs are implemented, and, like Japan, implementation is varied, suggesting that there are significant SPP implementation barriers exist even across rigid and flexible regulatory settings. As a consequence, local climate mitigation programs have not reached their potential, and markets have been slow to increase their delivery of sustainable products. These issues are concerns that the United Nations Environmental Programme, the International City/County Management Association, the Sustainable Purchasing Leadership Council, and the OECD state need to be resolved if we are to move towards a low GHG economy. While aspects of SPP implementation have been studied in the European Union, they lack consideration in Japan and the U.S., and virtually no scholarly cross-comparative studies exist outside of Europe, even though thousands of SPPs are implemented outside the European Union. This latter issue is particularly important because variations in regulatory settings are likely to impact the effectiveness of SPP outcomes. This study utilizes a three-tiered approach to assess SPP implementation. The first is a multicity survey of the facilitators/inhibitors of SPP implementation that compares leading SPP cities in Japan to non-leading cities. The second is an assessment of Japanese cities' written SPPs. Third, is a Japan-U.S. comparison of how the facilitators/inhibitors of SPP implementation and the cities' written SPPs differ between these two countries. The results will: (1) Offer critical insights about which factors facilitate/inhibit local SPP implementation in Japan (as compared to the U.S.), and SPPs' potential to facilitate a low GHG economy. The findings will be relevant to researchers in several disciplines, including public administration, public policy, management, and environmental sciences/management; (2) Generate recommendations for immediate actions that local governments can undertake to facilitate their SPP implantation that will be compiled in a user-friendly guidance report on SPP best practices that is distributed online to local government managers, procurement officers, sustainability officers, and professional networks; (3) Foster international collaboration on high impact use-inspired research in such a way that deepens our mutual understanding of SPPs across different institutional and cultural settings; (4) Develop international policy-relevant research that addresses pressing global concerns related to sustainability, which are a central focus of Abe's research agenda.