A front line (alternatively front-line or frontline) in military terminology is the position(s) closest to the area of conflict of an armed force's personnel and equipment, usually referring to land forces. When a front (an intentional or unintentional boundary) between opposing sides forms, the front line is the area where each side's forces are engaged in conflict. Leaders have often fought at the front lines either purposefully or due to a collapse in battle formation. While a calculated risk, fighting on the front has in instances reduced communication and heightened morale. The front is in direct contrast to the rear, which is the position farthest from conflict.

All branches of the United States Armed Forces use the related technical terms, Forward Line of Own Troops (FLOT) and Forward Edge of Battle Area (FEBA). These terms are used as battlespace control measures that designate the forward-most friendly maritime or land forces on the battlefield at a given point in time during an armed conflict. FLOT/FEBA may include covering and screening forces. The Forward Line of Enemy Troops (FLET) is the FEBA from the enemy's perspective.