Close Quarters Battle (CQB) or Close Quarters Combat (CQC) is a type of fighting in which small units engage the enemy with personal weapons at very short range, potentially to the point of hand-to-hand combat. In the typical CQB scenario, the attackers try a very fast, violent takeover of a vehicle or structure controlled by the defenders, who usually have no easy way to withdraw. Because enemies, hostages/civilians, and fellow operators can be closely intermingled, CQB demands a rapid assault and a precise application of lethal force. The operators need great proficiency with their weapons, but also the ability to make split-second decisions in order to avoid or limit friendly casualties. CQB is defined as a short-duration, high-intensity conflict, characterized by sudden violence at close range.

Criminals sometimes use CQB techniques, such as in an armed robbery or jailbreak, but most of the terminology comes from training used to prepare soldiers, police, and other authorities. Therefore, much CQB material is written from the perspective of the authorities who must break into the stronghold where the opposing force (opfor) have barricaded themselves.

Although there is considerable overlap, CQB is not synonymous with urban warfare, now sometimes known by the military acronyms MOUT (military operations on urban terrain), FIBUA (fighting in built-up areas) or OBUA (Operations in Built Up Areas) in the West. Urban warfare is a much larger field, including logistics and the role of crew-served weapons like heavy machine guns, mortars, and mounted grenade launchers, as well as artillery, armor, and air support. In CQB, the emphasis is on small infantry units using light, compact weapons that one man can carry and use easily in tight spaces, such as carbines, submachine guns, shotguns, pistols, and knives. As such, CQB is a tactical concept that forms a part of the strategic concept of urban warfare, but not every instance of CQB is necessarily enveloped urban warfare – for example, jungle and guerilla warfare are potential stages for CQB.