This set of four lectures was originally given at the VI Training Course in the Physics of Correlated Electron systems and High-Tc Superconductors, at Vietri Sur Mare, Italy (Oct 2001). The lectures are at an introductory level with exercises. The course describes the physics of moment formation, the Kondo effect and the development of a coherent heavy electron fluid in the dense Kondo lattice. The last lecture discusses the open problem of quantum criticality in heavy electron systems.

Revised references and corrections