Publisher Summary This chapter describes various aspects of radiological contrast agents. Iodinated water-soluble contrast media are used to enhance diagnostic information provided by radiographic examinations. They are of four types, including high-osmolar ionic monomers, low-osmolar ionic dimers, and low-osmolar nonionic monomers. Ultrasound contrast agents are microbubbles that provide acoustic enhancement. Contrast agents that enhance the diagnostic information provided by magnetic resonance imaging are mainly gadolinium-based, but nongadolinium paramagnetic contrast agents have also become available. The use of sodium bicarbonate infusion alone or in combination with a large dose of acetylcysteine in preference to isotonic saline has not been conclusively confirmed. The evolution of residual renal function 2 weeks after iodinated contrast medium administration has been evaluated in 36 patients on stable peritoneal dialysis, and compared with that in a control group of 36 patients who did not receive contrast medium. The safety of the low-osmolar contrast medium iobitridol in the general population and at-risk patients has also been investigated in a post-marketing surveillance study of 52,057 patients.