Increasing demographic pressure can lead to an increase in urban sprawl, which challenges the principles of sustained development. It enhances both displacement and loss of green space. Urban planners have to design space while allowing for increases in population density. Most of the time this is achieved by using space above the ground or in urban wastelands. Underground development can contribute but is rarely used to its full potential. This study investigates the reasons for the absence of underground development in urban planning and focuses on three aspects : Law : Swiss law defines property limits and underground usage. These limits depend on the underground's four resources : space, water, geothermal power and geomaterials. These resources define to what extent underground space can be used. Sociology : Understanding and analyzing perceptions and fears caused by underground space will help in ameliorating problems with space design and setting up priorities to be observed by urban planners. Economy : building underground seems more expensive than above the ground. This study will test this hypothesis. To investigate economic feasibility, it is important to know differences of costs as well as to identify factors accounting for increased costs. In Switzerland, building opposition significantly delays or prevents construction. Therefore, public opinion is a key factor in the planning of underground space. A case study will demonstrate the consequences of such oppositions. Finally, results of different studies will be compiled and analyzed in order to help authorities identify rules to observe, opportunities to seize and pitfalls to avoid.