These lectures are an extremely condensed version of the theory of Goldstone
bosons, with general features illustrated using a simple model. A more
comprehensive version of these lectures, which includes a general discussion of
effective theories of Goldstone bosons, including applications to the
low-energy behaviour of pions, spin waves (in antiferromagnets and
ferromagnets), and to the SO(5) proposal for high-T_c superconductors may be
found in hep-th/9808176.