Bergfried (plural: bergfriede; English: belfry; French: tour-beffroi; Italian: torrione; Castilian: torre del homenaje) is a tall tower that is typically found in castles of the Middle Ages in German-speaking countries and in countries under German influence. Stephen Friar in the Sutton Companion to Castles describes a bergfried as a "free-standing, fighting-tower". Its defensive function is to some extent similar to that of a keep (also known as a donjon) in English or French castles. However, the characteristic difference between a bergfried and a keep is that a bergfried was typically not designed for permanent habitation.

The living quarters of a castle with a bergfried are separate, often in a lower tower or an adjacent building called a palas (an English-style keep combines both functions of habitation and defence.) Consequently, a bergfried could be built as a tall slender tower with little internal room, few vaults and few if any windows. The bergfried served as a watchtower and as a refuge during sieges (at least if the siege was relatively brief). The distinction between a bergfried and a keep is not always clear-cut, as there were thousands of such towers built with many variations. There are some French keeps with only austere living quarters, while some late bergfrieds in Germany were intended to be habitable (Piper 1900).

For maximum protection, the bergfried could be sited on its own in the centre of the castle's inner bailey and totally separate from the enceinte. Alternatively, it could be close to or up against the outer curtain wall on the most vulnerable side as an additional defence, or project from the wall. For instance, the Marksburg has its bergfried in the centre, and Katz Castle on the most likely direction of attack. Some, like Münzenberg and Plesse Castles, have two bergfrieds.

Outside Germany, the crusader castles of Montfort Castle and Khirbat Jiddin built by the Teutonic Order had prominent towers that some authors have compared to bergfrieds (Kennedy 2000, Folda 2005), arguing that these castles depended more on Rhineland than local crusader traditions of military architecture.

Eynsford Castle in Kent is a rare English example, where the bergfried is the central element of the design.

The word '"bergfried", sometimes rendered perfrit, berchfrit or berfride and many similar variants in medieval documents, did not just refer to a castle tower, but was used to describe most other types of tower, such as siege towers, bell towers (cf. its cognate belfried or belfry) or storage buildings. The main tower of a castle was often simply referred to as a "tower" (Turm) or "big tower" (großer Turm). In late medieval Low German documents, however, the terms berchfrit, berchvrede and similar variants often appeared in connexion with smaller castles.

German castle research during the 19th century introduced Bergfried or Berchfrit as the general term for a non-residential main tower, and these terms then became established in the literature.

The etymological origin of the word is unclear. There are theories about it being derived from Middle High German or Latin, or even from a Greek word brought back from the Crusades. A theory that is often stated in older texts, that the bergfried took its name from the phrase "weil er den Frieden berge" ("because it keeps the peace"), i.e. it guaranteed the security of the castle, cannot be confirmed.