Green infrastructure (GI) revitalizes vegetation and soil, restores hydro-ecological processes destroyed by traditional urbanization, and naturally manages stormwater on-site, offering numerous sustainability benefits. However, despite being sustainable and despite being the object of unrelenting expert advocacy for more than two decades, GI implementation remains slow. On the other hand, the practice of traditional gray infrastructure, which is known to have significant adverse impacts on the environment, is still ubiquitous in urban areas throughout the world. This relationship between knowledge and practice seems unaccountable, which has not yet received adequate attention from academia, policy makers, or research communities. We deal with this problem in this paper. The specific objective of the paper is to explore the barriers to GI, and suggest policies that can both overcome these barriers and expedite implementation. By surveying the status of implementation in 10 US cities and assessing the relevant city, state and federal policies, we identified 29 barriers and grouped them into 5 categories. The findings show that most of the barriers stem from cognitive limitations and socio-institutional arrangements. Accordingly, we suggest 33 policies, also grouped into 5 categories, which span from conducting public education and awareness programs to changing policies and governance structures.