This text presents two readings of the institutional characteristics of financial capitalism through the works of J. M. Keynes before the crisis of 1929 and the research of D. Mackenzie on the conceptualization and the use of the derivative products in the United States after the Second World War. Three dimensions of their work will be put forward: a criticism of the orthodox vision of finance which regards the financial markets as effective and transparent mechanisms of allowance; an analysis of the institutional transformations of the financial sphere and an explanation of the instability of the financial markets centered on the role of collective factors. Work of Keynes and Mackenzie thus contributes to clarify the social and political nature of the mechanisms which underlie the current process of financiarisation of economic relations.