1 Introduction.- 2 Properties of Supercritical and Near-Critical Gases and of Mixtures with Sub- and Supercritical Components.- 3 Supercritical Gases as Solvents: Phase Equilibria.- 4 Heat and Mass Transfer.- 5. Solvent cycle.- 6 The Separation of Solvent and Dissolved Substances: Methods for Precipitation.- 7 Extraction of Substances with Supercritical Fluids from Solid Substrates.- 8 Countercurrent Multistage Extraction.- 9 Chromatography with Supercritical Fluids (Supercritical Fluid Chromatography, SFC).- 10 Conclusion.