Conventional water‐soluble iodine‐containing contrast media such as salts of diatrizoic and iothalamic acids dissociate in solution resulting in preparations which are very high in osmolality. Intravascular or intrathecal injections of these compounds therefore represent severe physicochemical insult to the body, with many associated side effects. Contrast media with lower osmolalities have been produced in two ways: first by producing compounds which do not dissociate in solution (metrizamide, and more recently iopamidol and iohexol), and second by creating dimers (ioxaglate). These media provide significant clinical advantages over the conventional, hyperosmolar media. A new class of nonionizing dimers with even lower osmolalities are currently being investigated. This paper reviews the development of the low osmolar media, their advantages, and their use in medical and veterinary radiol