This paper addresses the process towards the integration of subsurface knowledge into urban planning for three cities – Rotterdam, Glasgow and Oslo – participating in the European Cooperation in Science and Technology (COST) Action TU1206 Sub-Urban. These cities each have unique challenges in managing conflicts and opportunities in the subsurface in the planning process. The COST Sub-Urban Action has enabled a unique interaction between subsurface specialists and urban planners across over 20 European cities, and has laid the foundations for a new understanding between experts who develop subsurface knowledge and those who can benefit most from it – urban planners and decision makers. Common challenges identified include: improving planning policies, enhancing the level of awareness of the subsurface in city development and the modification of legislation to include the subsurface. The paper provides a review of the current status of subsurface planning in the three cities, each of whom are aiming to adapt their urban planning practice and legislation in light of emerging subsurface knowledge, and the current major knowledge gaps. In our opinion, there are two main routes to raise awareness that lead to improved understanding and the use of subsurface information in urban planning processes: (1) the development of a subsurface policy and (2) providing subsurface information. These measures should enable subsurface knowledge to be widely disseminated in order to manage risks and opportunities, and maximise the economic, social and environmental benefits of the urban subsurface and its services on which cities depend.