Mountains form the backbones of many landscapes around the globe, posing unique problems for urban construction and maintenance. As populations grow, cities continue to expand into mountainous areas that are unsuitable for building, causing geological hazards, erosion, increased runoff, landscape destruction, river siltation, and floods. The United States was one of the first countries to regulate hillside development at the legislative level, and a series of survey reports based on multiple cases have emerged, but no single report can cover the entire U.S. territory. The paper presents a comparative analysis of seven survey reports published before the end of 2020, and uses a combination of narrative literature review, qualitative GIS, and personnel interviews to sort out the purposes and implementation strategies of hillside development regulations in the United States. The paper finds that the core of hillside development regulations in the United States lies in balancing three pairs of contradictions and promoting sustainable mountain development in a relatively flexible and resilient manner. Finally suggests a cross-sectional comparison and systematic summary of relevant measures in China to expand and challenge the existing knowledge on hillside development regulations and help construct a national spatial use regulation system in the new era.