Thorium, a naturally occurring radioisotope, and thorium compounds, primarily where thorium is present in the +4 oxidation state, are discussed. The main interest in thorium is as a nuclear fuel, but thorium and its compounds have many specialty uses, for instance, as gas, lantern mantels, and catalysts. Thorium has a rich coordination and organometallic chemistry. A drawback to using thorium in many processes is the chemical reactivity of the metal as well as the inherent radioactivity of all thorium isotopes. Health and safety factors essential for working with thorium are discussed.