2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/148195This is an introduction to the method of effective field theory. As an application, I derive the effective field theory of low energy excitations in a conductor, the Landau theory of Fermi liquids, and explain why the high-$T_c$ superconductors must be described by a different effective field theory.39 pages, LaTeX. Lectures presented at TASI 1992. Figures now included in epsf formHigh Energy Physics - TheoryCondensed MatterHigh Energy Physics - LatticeHigh Energy Physics - Phenomenologytext