The paper offers an analysis of Urban Underground Space (UUS) use and its influence on cities' sustainability. It has been widely recognized that urban land is a valuable resource. During recent decades UUS, especially in big cities, has become a scarce and valuable resource. This paper outlines UUS use, including some quantitative descriptors and an analysis of its historical evolution. Historic top-down development of Urban Underground Infrastructure (UUI) and shortcomings in its planning have resulted in a lack of available UUS for new developments. A sectoral approach to UUS development and UUS availability on a first-come-first-served basis does not allow the full benefits that UUI can provide for urban sustainability. This paper recognizes UUS as a valuable non-renewable resource, which requires careful consideration during city planning. It focuses on the need and opportunities for mainstreaming UUS into cities' Master plans. To facilitate this, UUS services are listed and classified; their characteristics are identified and discussed. UUS users are also identified and possible conflicts between them are discussed. State-of-the-art consideration of UUS in cities' Master plans is critically analyzed and suggestions are made for mainstreaming UUS and sustainability issues into Master plans. It is recommended that the following are implemented: three-dimensional planning; prioritizing UUS services; studying prospective functional and spatial interrelations between different types of infrastructures; and integrated assessment.