Book excerpt: The systematic investigation of self-diffusion and impurity diffusion in metals began as a result of the availability of a wide variety of artificial radio- isotopes following the Second World War. During the following years, rapid advances in the theory of solid-state diffusion and the ever-increasing number of experimental data were comprehensively described in any number of textbooks and review papers. But impurity diffusion in metals was more or less superficially treated in the textbooks, and some of the review papers, with the result that - even up to now - a comprehensive review of the correct interpretation of impurity diffusion in metals has been lacking.