Public debt-to-GDP ratios have undergone substantial fluctuations over both the short and long term. Most recently, global debt-to-GDP ratios peaked at 100% on average in 2020 due to COVID-19, retracting substantially by 2022. To understand what drives these movements, we propose a structural approach to debt decompositions based on a SVAR identified with narrative sign restrictions. We find that GDP growth shocks and the corresponding comovements of macroeconomic variables are the key drivers of debt to GDP, accounting for 40% of the observed yearly variation in 17 advanced economies since the 1980s. […]