A frontline is a line of confrontation in an armed conflict, most often a war. On either side of the frontline stand the forces of the various combatants. In modern warfare, due to the broken nature of mechanized combat, frontlines rarely form; instead a zone of confrontation comprises a wide band where forces engage in battle.

World War I featured the most clearly defined frontlines known to date: the frontline in France became marked by dug trenches almost throughout.

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Frontline also names an Australian television series, and an American television series.