Sigma

Sigma may refer to:
 * Ood Sigma (TV: Planet of the Ood)
 * Sigma (letter)
 * Sigma (planet) (COMIC: The Fabulous Idiot)
 * Earl Sigma (TV: The Happiness Patrol)
 * Theta Sigma (TV: The Armageddon Factor, The Happiness Patrol, COMIC: Flashback)
 * Survey Ship Sigma (COMIC: The Dalek Project)