Supply lines are roads, rail, and other transportation infrastructure needed to replenish the consumables that a military unit requires to function in the field.

Modern military units consume large quantities of such consumables and can be rendered combat-ineffective in hours or days if supplies are interdicted. This vulnerability has led many military leaders to build doctrine around indirect approaches to the enemy from the rear or above. These have been known as: "envelopment", "vernichtungsgedanken", "blitzkrieg", "hyperwar", and other forms.