The COVID-19 pandemic has tested many countries’ health systems to – and beyond – their limits and highlighted the interdependence of health with other sectors at both the national and global level. However, even before the pandemic, health systems faced challenges to their resilience and sustainability. Against this backdrop, the Partnership for Health System Sustainability and Resilience (PHSSR) was formed by the World Economic Forum, AstraZeneca and the London School of Economics in Summer 2020. Currently in its pilot phase, the driving purpose of the Partnership is to improve global health by providing qualitative and quantitative evidence to inform policy, and promote action at national and international levels to strengthen health system sustainability and resilience. PHSSR’s objectives are as follows: Build knowledge, understanding, and consensus on the dimensions of, and the relationship between health system sustainability and resilience, so that they can be understood in different country contexts, enabling identification of strengths, weaknesses, opportunities, and threats. Guide action by generating evidence-informed solutions and policy recommendations to improve sustainability and resilience, promoting their uptake and supporting pilot implementation of the framework in each country. Facilitate national, cross-border and cross-sectoral learning and evidence-informed action to strengthen health system sustainability and resilience, based on the knowledge and relationships built through this partnership. Published to coincide with PHSSR’s inaugural summit, taking place on March 15 – 19 2021, this interim report of the PHSSR’s pilot phase sets out how PHSSR has conceptualised health system sustainability and resilience, and presents the initial Framework that was used to guide the development of a set of system-level Country Reports in the pilot phase. It also presents a summary of the key themes and recommendations that have emerged in those reports, and a preliminary assessment of the application of the Framework, identifying areas in which it can be strengthened. Following a full evaluation of the pilot phase, this report will be followed by a final report, including an updated version of the Framework, pointing the way for the Partnership’s future development.