A blockade runner is a merchant vessel used for evading a naval blockade of a port or strait. It is usually light and fast, using stealth and speed rather than confronting the blockaders in order to break the blockade. Blockade runners usually transport cargo, for example bringing food or arms to a blockaded city. They have also carried mail in an attempt to communicate with the outside world.

Blockade runners are often the fastest ships available, and come lightly armed and armored. Their operations are quite risky since blockading fleets would not hesitate to fire on them. However, the potential profits (economically or militarily) from a successful blockade run are tremendous, so blockade-runners typically had excellent crews. Although having modus operandi similar to that of smugglers, blockade-runners are often operated by state's navies as part of the regular fleet, and states having operated them include the Confederate States of America during the American Civil War, and Germany during the World Wars.