Due to their irreversible nature, the development of underground spaces should be properly investigated, planned and managed in order to contribute to sustainable development in cities. In many cities, there is a lack of a holistic planning approach with clear policy and supportive administrative guidelines to utilize this alternative spatial solution, resulting in lack of incentives with underground development projects often being carried out on singleproject basis. Tapping the experience in two densely populated cities in Asia, Hong Kong and Singapore, this paper therefore aims to examine the significant, yet often neglected, urban planning and design issues relating to the development of underground spaces for coordinated and balanced utilization of this underground spatial resource. 