D-Cysteinolic acid is a zwitterionic aminosulfonate found in marine (and occasionally freshwater) environments. It is distributed in a wide range of algae (red, green and brown algae and diatoms), and some bacteria and sea animals. It was discovered in 1957 and in spite of its long history, its biosynthesis and degradation is poorly understood. Cysteinolic acid is found conjugated to steroids, lipids and arsenosugars, and the cysteinolic acid motif is found within the structures of various capnoid and sulfoceramide sulfonolipids. This review provides an historical account of the discovery of D-cysteinolic acid and related molecules, its distribution and occurrence within marine and freshwater organisms, routes for its chemical synthesis, and summarizes knowledge and speculations surrounding its biosynthesis, degradation and bioconversions.