Ever since the crisis of 2008, the dynamism and self-referentiality of financial markets have puzzled observers. This article argues that this dynamism is the product of a long process of commensuration, by which ever more heterogeneous financial assets and financial instruments have come to be compared with, substituted for, and valuated relatively to one another, and have thereby been condensed into a highly interconnected financial system. This trajectory can be found both in the long-term historical emergence of financial markets from ancient origins and in the more recent transformations of the financial system since the 1970s, including (i) the rise of derivatives markets, and (ii) the rise of capital markets as against bank-intermediated capital flows. The rise of derivatives markets was triggered by the commensuration of basic securities (such as stock, bond) and derivatives (such as options, futures), established by the Black-Scholes-Merton theory of option pricing. The rise of capital markets was rooted in the commensuration – and hence, competition and substitution – of bank products (such as loans, deposits) and non-bank products (capital market securities).