Economics was conceived as early as the classical period as a science of causes. The philosopher–economists David Hume and J. S. Mill developed the conceptions of causality that remain implicit in economics today. This article traces the history of causality in economics and econometrics, showing that different approaches can be classified on two dimensions: process versus structural approaches, and a priori versus inferential approaches. The variety of modern approaches to causal inference is explained and related to this classification. Causality is also examined in relationship to exogeneity and identification.