Naval boarding action is an offensive tactic used in naval warfare to come up against (or alongside) an enemy marine vessel and attack by inserting combatants aboard that vessel. The goal of boarding is to invade and overrun the enemy personnel on board in order to capture, sabotage or destroy the enemy vessel. While boarding attacks were originally carried out by ordinary sailors who are proficient in hand-to-hand combat, larger warships often deploy specially trained and equipped regular troops such as marines and special forces as boarders. Boarding and close quarters combat had been a primary means to conclude a naval battle since antiquity, until the early modern period when heavy naval guns gained tactical primacy at sea.

A cutting out boarding is an attack by small boats, preferably at night and against an unsuspecting, and anchored, target. It became popular in the later 18th century, and was extensively used during the Napoleonic Wars. This heralded the emphasis on stealth, and surprise, that would come to dominate future boarding tactics. An example is the successful cutting out of the Hermione which took place at Puerto Cabello, Venezuela, on 25 October 1799.

In modern warfare, boarding by military forces almost always involves stealth, and usually takes place at night. It may involve the use of small submarines or submersibles, or inflatable boats, or by frogmen. All involve scaling the sides of the ship. When stealth is not as important, helicopters may be used to carry troops to the deck of the ship.