Rhodium is a silvery-white transition metal. It holds the distinction of being the world's most expensive precious metal. It has an atomic number of 45 and is about as nonreactive as gold. The only way to dissolve rhodium is with sulfuric acid. Part of rhodium's appeal comes from its high reflectance, almost unique among the metals. It is sometimes used as an expensive and flashy alternative to silver in jewelry, on which it is sometimes plated. Some of the most expensive consumer items in the world are made from rhodium.

Rhodium was discovered in 1803 by William Hyde Wollaston, who isolated it from platinum. He named it after the Latin rhodon, meaning rose. Wallaston was also the discoverer of palladium.

Rhodium costs about six times as much as gold by weight. It is never found in mineral form, only being found in trace amounts within platinum or nickel ores. 80% of the world's rhodium comes from South Africa, and world production of the metal is only about 20 tons per year.

Rhodium is a fission product in the decay of the isotope uranium-235, but only about 1% by weight, and most nuclear fuels only contain about 3% uranium-235, meaning only 1% of 3% of nuclear waste consists of rhodium. Despite rhodium's great value, the cost of separation is generally greater.

Rhodium has twenty-five known isotopes in all, most with a half-life of less than an hour. This quantity of isotopes is typical among elements with atomic numbers in this range. Rhodium compounds exist, but not outside of the laboratory. They are highly poisonous.

Rhodium was made famous in 1979 when the Guinness Book of World Records awarded Paul McCartney a rhodium-plated disc to celebrate his status as history's all-time best-selling songwriter and recording artist. Rhodium is used when other precious metals such as silver, gold, or platinum are considered not enough.