This project reviewed and summarized the current literature by Theofanis P. Mamuneas (2008) and Mamuneas with M. Ishaq Nadiri (2003) on the returns to highway investments. The author provided an overview of the conceptual relationship between highways and output, described the highway capital stock estimated by Fraumeni and used by Mamuneas, and analyzed the results for consistency within the modeling framework and in context with other studies. The author then briefly summarized the broad range of estimates from the literature to add additional context and included a list of issues that still need to be addressed.