This paper presents the IMF’s systemwide stress testing approaches, which cover multiple financial sub-sectors and their clients. Developing these tools is crucial for identifying cross-sector and cross border amplification channels and enhancing policy responses, as recognized by the international financial stability community. The paper reviews classic and modern theories and operational methods for analyzing systemic liquidity risks that impact numerous institutions simultaneously, illustrating how shocks can spread through banks, nonbank financial institutions (NBFIs), and market-based finance via runs, redemptions, margin and collateral calls, fire sales, price dynamics, and disruptions in core markets. It details two base IMF tools—an Excel-based flow-of-funds framework and investment fund liquidity analysis with fire sale and market-impact dynamics—and their application and enhancement within Financial Sector Assessment Programs (FSAPs) across various countries.