Helping countries to improve the lives of their citizens requires effective international development co-operation. The Global Partnership for Effective Development Co-operation's principles (country ownership, focus on results, inclusive partnerships, and transparency and mutual accountability) have been guiding relationships between development partners for close to a decade, helping them to strengthen and improve the way they co-operate and ensuring that all citizens are invested in the process. The Organisation for Economic Co-operation and Development (OECD) and the United Nations Development Programme (UNDP) work together to monitor progress in using these principles. In 2018, data was collected by 86 partner countries and territories, in collaboration with more than 100 development partners, to serve as the basis for this work and provide evidence. By highlighting where progress has been made and where challenges remain, the work helps governments and their partners strengthen collective action towards the 2030 Agenda for Sustainable Development.