The notion that the international monetary system is hierarchical has become increasingly common, but the nature, causes, and shape of international monetary hierarchy remain vague. In this article, we develop a monetary theory of international hierarchy based on the “key currency” approach. We perceive the international monetary system as a world-spanning payment system that is inherently hierarchical because it needs central nodes for clearing and settlement. The centrality of the US-Dollar (USD) as global key currency places the US at the apex and makes the Federal Reserve (Fed) the system’s hierarchically highest institution. Other monetary jurisdictions are pushed into peripheral positions and rely on both using and creating USD-denominated credit money instruments “offshore.” Based on this approach, we explain international monetary hierarchy through different mechanisms to supply emergency USD liquidity from the Fed to non-US central banks. Currently, there are three different public mechanisms for non-US central banks to access the Fed’s balance sheet and attain emergency USD liquidity. The first-layer periphery may receive emergency USD liquidity via the Fed’s central bank swap lines. The second-layer periphery can make use of the Fed’s new repo facility for Foreign and International Monetary Authorities to access emergency USD liquidity. The residual mechanism for the third-layer periphery to access emergency USD liquidity is the Special Drawing Rights system, administered by the International Monetary Fund, in which the Exchange Stabilization Fund acts as gatekeeper for the Fed.