Thirty years of heavy fermions: Scientific setting for their discovery and partial understanding

Heavy Fermions provide an extreme example of the utility of the idea of continuity and analyticity in physics. Their discovery and study in the past 30 years has added a fascinating chapter to condensed matter physics. I briefly review the origins of the heavy-fermion problem out of the study of magnetic moments in metals and the study of mixed-valent rare-earth compounds. I also review the principal ideas underlying the features understood in their Fermi-liquid phase as well as in their anisotropic superconductivity. The unsolved issues are also briefly mentioned.