Organic chemistry is the study of chemical compounds that contain carbon. Carbon has the ability to form a chemical bond with a wide variety of chemical elements and other carbon atoms. This allows a nearly unlimited number of combinations, called organic compounds. The subject of carbon compounds is called organic chemistry because all known organisms, or living things, are made up of water and carbon compounds. Organic chemistry largely involves the synthesis, or formation, of organic products by chemical reaction using different reactants and reagents, the substances used up during a reaction. Several different areas of chemistry expand on the concepts and principles of organic chemistry, including biochemistry, microbiology, and medicine.