This paper examines the continued growth in the use of underground space beneath cities and the widespread lack of significant and broad planning efforts for its use. The paper is drawn from the collective experience and prior research of the authors together with information exchanges afforded by the activities of the International Tunnelling and Underground Space Association's Committee on Underground Space (ITACUS). The particular focus of this paper is on sustainability issues related to urban underground space use including contribution to an environmentally sustainable and aesthetically acceptable landscape, anticipated structural longevity and the maintenance of opportunity for urban development by future generations. However, owing to their initial cost and permanent alteration of the underground environment, underground structures put a special emphasis on long-range planning which considers life-cycle cost-benefits and the selection of projects that offer the highest contribution to urban sustainability rather than a short-term fix to an individual need.