somewhere gives an incorrect result. I want to show you that the existence of sum rules in many cases follows rigorously from QCD. Often the difficulty is not in the sum rule itself, but rather on how to use it in practice, when one is dealing with a channel where there is very little direct experimental information. We shall see that it is important to check that the matching of the input low energy hadronic [*ansatz*]{} to the continuum described by perturbative QCD (pQCD) satisfies [*global duality*]{} tests.

The lectures are organized as follows. I shall start in section \[sec:srptqcd\] with an introduction to sum rules which were derived prior to the development of QCD. This section is mostly descriptive and assumes some familiarity with topics like chiral perturbation theory which are covered in other lectures [@PiclesH; @ManlesH] at this school, and with dispersion relations. The reader who has never heard of dispersion relations should first read the beginning of section \[sec:disperrels\] and section \[subsec:vpmf\], and then go back to section \[sec:srptqcd\]. Section \[sec:ttpfsr\] contains quite a few technical details. It should be useful to those who want to learn how to use QCD sum rules in practice. Section \[sec:nppc\] 