The Decomposition Temperature of a substance is the temperature at which the substance decomposes into smaller substances or into its constituent atoms.

Some compounds dissociate into smaller compounds. For example, Calcium Carbonate dissociates into Calciun oxide and carbon dioxide.

Some compouds, on the other hand simply dissociate into their constituent atoms. Water, when heated to well over 2000 degrees Celsius, breaks up into hydrogen and oxygen atoms.