The aim of Albert Aftalion’s Periodic Crises of Overproduction is to lay the analytical building blocks of a medium-term approach to the theory and policy of economic fluctuations. Aftalion builds his theory on a disaggregated (structural) representation of the economic system that overcomes the conventional micro-macro dichotomy. This analysis eschews both the explanation of crises in terms of cumulative processes triggered by long-term factors and that in terms of purely contingent mismatches and ruptures. Aftalion highlights features such as lack of synchronization between sectors, different time horizons between socio-economic groups, and dissimilar speeds of change between production and consumption units. His approach draws key analytical concepts (such as the accelerator principle) from a detailed investigation of the interdependencies and temporal asymmetries of an industrial economy. It is an enlightening complement to Keynes’ General Theory.