This report contributes to the broader international debate on why we need multilateralism and how to make it more effective to achieve the 2030 Agenda. At a time when the value of multilateralism is being questioned, the report provides new evidence and recommendations for a new “pact." This report presents new evidence on how multilateral development co-operation is evolving, including because of a growing number of actors - governments, philanthropists, private sector and others - engaging with the multilateral development system. The report outlines policy recommendations to help all actors support a stronger and more effective multilateral system through evidence-based Principles of Good Multilateral Donorship. These principles can be the basis of a new pact on multilateralism needed to achieve the 2030 Agenda.