City-to-city partnerships and decentralised development co-operation (DDC) can play a key role in advancing the SDGs and in addressing global megatrends, the aftermath of the COVID-19 pandemic and other shocks. This report discusses the framework conditions for effective city-to-city partnerships and takes stock of existing monitoring and evaluation mechanisms. As a complement, it proposes a systemic monitoring and evaluation framework for city-to-city partnerships to localise the SDGs, combining self-assessment and SDG indicators. This framework aims to bridge the gap in terms of measuring the progress of cities engaged in partnerships on the 2030 Agenda and their compliance with the G20 Rome High-Level Principles on city-to-city partnerships for localising the SDGs. The report also presents lessons learned from a pilot-testing of this new framework and highlights policy implications and ways forward to enhance the sustainability, transparency and accountability of city-to-city partnerships, in a shared responsibility across levels of government and stakeholders.