The article explores the relationship between co-integration and error correction models in economics. It introduces a method to estimate and test these models, showing that when certain time series are co-integrated, deviations from equilibrium are stationary. The study proposes a two-step estimator for estimation and formulates seven statistics for testing co-integration. Through empirical examples, it is found that consumption and income are co-integrated, while wages and prices are not. Additionally, short and long interest rates are co-integrated, and nominal GNP is co-integrated with M2 but not with M1, M3, or aggregate liquid assets.