Urban warfare is warfare in urban areas such as towns and cities. Urban combat differs from combat in the open at both operational and the tactical levels. Complicating factors in urban warfare include the presence of civilians and the complexity of the urban terrain. Urban combat operations may be conducted to capitalize on strategic or tactical advantages associated with the possession or the control of a particular urban area or to deny these advantages to the enemy. It is arguably considered to be the most difficult form of warfare.

Fighting in urban areas negates the advantages that one side may have over the other in armor, heavy artillery, or air support. Ambushes laid down by small groups of soldiers with handheld anti-tank weapons can destroy entire columns of modern armor (as in the First Battle of Grozny), while artillery and air support can be severely reduced if the "superior" party wants to limit civilian casualties as much as possible, but the defending party does not (or even uses civilians as human shields).

Some civilians may be difficult to distinguish from such combatants as armed militias and gangs, and particularly individuals who are simply trying to protect their homes from attackers. Tactics are complicated by a three-dimensional environment, limited fields of view and fire because of buildings, enhanced concealment and cover for defenders, below-ground infrastructure, and the ease of placement of booby traps and snipers.

Historically, the United States Armed Forces has referred to urban warfare as UO (urban operations), but this term has been largely replaced with MOUT (military operations in urban terrain).

The British armed forces terms are OBUA (operations in built-up areas), FIBUA (fighting in built-up areas), or sometimes (colloquially) FISH (fighting in someone's house), or FISH and CHIPS (fighting in someone's house and causing havoc in people's streets/public spaces).

The term FOFO (fighting in fortified objectives) refers to clearing enemy personnel from narrow and entrenched places like bunkers, trenches and strongholds; the dismantling of mines and wires; and the securing of footholds in enemy areas.

Israel Defense Forces calls urban warfare לש"ב (pronounced LASHAB), a Hebrew acronym for warfare on urban terrain. LASHAB in the IDF includes large-scale tactics (such as use of heavy armoured personnel carriers, armoured bulldozers, UAVs for intelligence, etc.), close-quarters battle training for fighting forces (how a small team of infantry soldiers should fight in close and built-up spaces). IDF's LASHAB was developed mainly in recent decades, after the 1982 Lebanon War included urban warfare in Beirut and Lebanese villages, and was further developed during the Second Intifada (2000–2005) in which IDF soldiers entered and fought in Palestinian cities, villages and refugee camps. The IDF has an advanced facility for training soldiers and units in urban warfare.

Urban military operations in World War II often relied on large quantities of artillery bombardment and air support varying from ground attack fighters to heavy bombers. In the European theatre of war, roughly 40% of battles took place in urban areas. In some particularly vicious urban warfare battles such as Stalingrad and Warsaw, all weapons were used irrespective of their consequences.^{[citation needed]}