  We present a simple introduction to the techniques of effective field theory
(EFT) and their application to QCD. For problems with more than one energy
scale, the EFT approach is a useful alternative to more traditional
model-building strategies. The most relevant such problem for this discussion
is that of making contact between QCD and the hadronic phase of matter. As a
simple example, an EFT calculation of the bound states of hydrogen within QED
is sketched. A more significant demonstration of the power of EFTs, the
construction of the chiral Lagrangian and chiral perturbation theory, is also
included. The results provide us with the road map to a complete QCD-based
theory of nuclear matter at nonzero temperatures and densities, a vital
component to a quantitative understanding of the phase transition from hadron
gas to quark-gluon plasma.
