The Duchy of Gaeta is an early medieval state centered on the coastal South Italian city of Gaeta.

It begins in the early ninth century as the local community begins to grow autonomous as Byzantine power lags in the Mediterranean and the peninsula due to Lombard and Saracen incursions.The primary source for the history of Gaeta during its ducal period is the Codex Caietanus, a collection of charters preserving Gaetan history better and in greater detail than that of its neighboring coastal states: Naples, Amalfi, and Sorrento.

However, unlike these sister seaports, Gaeta is never a center of commercial importance.

In 778, it is the headquarters from which the patrician of Sicily directs the campaign against the Saracen invaders of Campania.