This course, lays out the underpinnings of public debt dynamics (i.e., of the evolution of public debt over time) and explains how these concepts are applied in the easy-to-use Excel-based Public Debt Dynamics Tool (DDT). The DDT provides public debt projections under a baseline and alternative scenarios, including through fan charts that represent the uncertainty about the evolution of public debt. The DDT also identifies the main drivers of public debt changes and computes fiscal adjustments paths that would be necessary to achieve a user-defined public debt target after a user-defined adjustment period.