A line of communication (or communications) is the route that connects an operating military unit with its supply base.

Supplies and reinforcements are transported along the line of communication. Therefore, a secure and open line of communication is vital for any military force to continue to operate effectively. Prior to the advent of the use of the telegraph and radio in warfare, lines of communication were also the routes used by dispatch riders on horseback and runners to convey and deliver orders and battle updates to and from unit commanders and headquarters. Thus, a unit whose lines of communication were compromised was vulnerable to becoming isolated and destroyed, as the means for requesting reinforcements and resupply is lost. The standard military abbreviation is LOC. There is also SLOC for Sea Line of Communication, GLOC for Ground Line of Communication, or ALOC for Air Line of Communication.

The interdiction of supplies and reinforcements to units closer to the front lines is therefore an important strategic goal for opposing forces. Some notable examples: