2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/195251We review the theory of inflation with single and multiple fields paying particular attention to the dynamics of adiabatic and entropy/isocurvature perturbations which provide the primary means of testing inflationary models. We review the theory and phenomenology of reheating and preheating after inflation providing a unified discussion of both the gravitational and nongravitational features of multi-field inflation. In addition we cover inflation in theories with extra dimensions and models such as the curvaton scenario and modulated reheating which provide alternative ways of generating large-scale density perturbations. Finally we discuss the interesting observational implications that can result from adiabatic-isocurvature correlations and non-Gaussianity.51 pages, latex, 16 figures, version to appear in Reviews of Modern PhysicsAstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - PhenomenologyHigh Energy Physics - Theorytext