A solvent is a liquid that becomes a solution by dissolving a solid, liquid, or gaseous solute. The most common solvent in everyday life is water. This book presents topical research data in the study of organic solvents, including co-solvent applications for biological systems; studying the structure of dehydrated proteins in the presence of organic solvents; the applications of Gram-positive bacteria in organic solvents; as well as the toxicity of organic solvents and ionic liquids to lactic acid-producing microbes.