Abstract
Reviewed at both a relatively elementary and more advanced level is the interpretative theory of the electron spin resonance of magnetic ions in metals. The various theoretical possibilities are illustrated by experimental examples wherever possible. Initially the development is based upon the Bloch-Hasegawa equations. The relationship of the advanced theory to this more elementary theory is emphasized. Multimagnetic-impurity experiments, the skin depth problem, the analysis of exchange, hyperfine and crystal field parameters, Redfield theory, ionic and virtual bound state models and the Kondo effect, all in relation to E.S.R. in metals, are each covered in some detail. A discussion of some outstanding problems and projections for the future are also included.