A cyclotomic number is a complex number that lies on and is one of a sequence of numbers that divides the unit circle in the complex plane into an equal number of parts. More generally, the term may be used for a complex number that is closely related to such a number.

The roots of unity, known as de Moivre numbers, are the most common cyclotomic numbers,. The Sylvester cyclotomic numbers are a more complicated variant related to Lucas sequences.