Nik Bhatia, a fixed income specialist and Bitcoin researcher, introduces a powerful analytical framework for understanding monetary systems by modeling them as hierarchical layers of money with different degrees of credit risk and finality. The framework reveals that all modern monetary systems operate in layers: central bank reserves and physical currency at the top layer (the most final and credit-risk-free), commercial bank deposits and government bonds at the second layer, and financial institution claims at lower layers. Bhatia applies this framework historically, showing how it illuminates the gold standard era — where gold was the first layer, Bank of England notes the second, and commercial bank deposits the third — and the transition to the dollar-based Bretton Woods system, and eventually the current dollar hegemony system anchored by the Federal Reserve. The framework's most provocative application is its analysis of Bitcoin as a potential new first-layer reserve asset and the implications of central bank digital currencies (CBDCs) for the architecture of the global monetary system. Bhatia argues that just as the dollar displaced gold as the world's primary reserve layer over the twentieth century, digital-native assets could displace fiat currencies as the first-layer anchor of a future monetary system. Accessible, analytically precise, and genuinely illuminating on monetary history, this is one of the clearest and most original contributions to the literature on money and Bitcoin.