The aim of this special issue of the American Journal of Analytical Chemistry (AJAC) on Supercritical Fluids is to promote knowledge about this rapidly developing area of analytical chemistry, which is very useful in fields such as the pharmaceutical and pesticide manufacturing industries, food production, clinical medicine and environmental studies. In this issue, the use of Supercritical Fluids (SFs) in Supercritical Fluid Extraction (SFE) and Supercritical Fluid Chromatography (SFC) is described.