The Opsikian Theme or simply Opsikion is a Byzantine theme (a military-civilian province) located in northwestern Asia Minor (modern Turkey).

Created from the imperial retinue army, the Opsikion is the largest and most prestigious of the early themes, being located closest to Constantinople.

Involved in several revolts in the 8th century, it is split in three after c. 750, and loses its former preeminence.

It survives as a middle-tier theme until after the Fourth Crusade.