''Microfoundations'' has become prominent in the discourse of management scholars. But what is it and how does it matter? This Element provides a characterization of microfoundations based on classical work on the methodology of social science and documents and discusses its manifestations in management research over the last one and a half decades. It also covers the relation of microfoundations to multilevel research, criticisms of microfoundations, and empirical research strategies for microfoundations.