Over the coming years, significant infrastructure investment will be required to sustain economic growth and improve well-being in many regions and cities. Subnational governments will have a key role to help provide this infrastructure - they are responsible for almost 60% of total public investment in G20 countries. This G20-OECD Policy Toolkit, developed with input from the Asian Development Bank, aims to support inclusive and quality infrastructure investment by subnational governments across developing, emerging and developed countries. It outlines key elements of creating an enabling environment for subnational infrastructure investment. It then details common and innovative funding sources, financing instruments and investment approaches. Rather than recommending specific instruments, it provides a ‘toolkit’ of options for policymakers and practitioners. The Policy Toolkit is supported by 23 case studies.