Effective Theories From Nuclear to Particle Physics.- Finite Temperature Field Theories: Review.- Divergences in the Perturbation Theory.- Optimized Perturbation Theory.- The Large-N Expansion.- Dimensional Reduction and Infrared Improved Treatment of Finite Temperature Transitions.- Thermodynamics of Strong Matter.- Finite Temperature Restoration of the Brout-Englert-Higgs Effect.- The Spectral Function.- Computation of the Basic Diagrams.- Integrals Relevant for Dimensional Reduction.