gives a qualitative introduction to non–perturbative power corrections. It should be helpful as an introduction to more technical papers quoted there. The two examples discussed in section \[sec:seqcdsr\] are rather topical subjects, much under discussion at the moment, and illustrate how to use the material covered in the previous sections.

There are a lot of topics on sum rules which are not mentioned in these introductory lectures like for example, applications to baryons, to heavy quark systems and gluonium. The curious reader should complement these lectures with extra reading. There are two references which contain a lot of material. One is the book by Stephan Narison [@Nar89]; the other is M.A. Shifman’s selection of some of the original articles with his comments in ref. [@Shi92].

Sum Rules prior to QCD {#sec:srptqcd}
----------------------

Sum rules in hadron physics have a long history. We shall be concerned in this section with various sum rules which were suggested before QCD was established as the theory of the strong interactions. I want to do this for two reasons: first, because they are interesting sum rules [*per se*]{} and second, because they illustrate very clearly the basic ingredients which go into the derivation of sum 