This policy brief examines the requirements for building effective transnational partnerships in different policy fields, based on the lessons learned from the recent Lighting Metropolis project – a cross-border innovation venture between Denmark and Sweden that sought to develop smart lighting solutions in urban environments. The brief begins with an overview of this new technology area, before outlining the main opportunities and challenges in the implementation of smart lighting throughout Europe. This is followed by a review of the key findings from Lighting Metropolis, with a focus on assessing the experiences of transnational co-operation identified during the project. Finally, the concluding section outlines a number of recommendations for enhancing transnational collaboration. The policy brief has been prepared by Nordregio as part of the BSR Stars S3 project. It is based on a literature review and interviews conducted with partners involved in Lighting Metropolis.