Achieving global agendas such as the Sustainable Development Goals requires substantial investment. As the level of government closest to citizens, subnational governments are uniquely positioned to direct investments toward sustainable development that aligns with local needs. However, many face financial constraints and lack the necessary expertise to secure funding and financing for sustainable urban development. City-to-city partnerships, a form of decentralised development co-operation, can offer a solution. By fostering peer-to-peer learning, facilitating knowledge exchange, and creating investment-friendly environments, these partnerships can help subnational governments overcome financial and capacity challenges. This paper explores how city-to-city partnerships can unlock funding and financing for sustainable urban development. It documents their role in strengthening local government capacity to enhance their investment readiness and mobilise financial resources. The paper also provides guidance on how national governments can create enabling conditions for city-to-city partnerships to thrive, ensuring these remain a critical tool for advancing global development goals.