How should economists model the relationship between macroeconomic phenomena and microeconomic structure? Economists have been struggling to answer this question for decades. Nevertheless, the Walrasian equilibrium model devised by the nineteenth century French economist Leon Walras (1834-1910) still remains the fundamental paradigm that frames the way many economists think about this issue. Competitive models directly adopt the paradigm. Imperfectly competitive models typically adopt the paradigm as a benchmark of coordination success. Although often critiqued for its excessive abstraction and lack of empirical salience, the paradigm has persisted.