攻城战是指对城堡、城市或要塞进攻的战争模式。依照战局模式另可分作巷战和包围战，目的可以是夺取建筑、资源、战略要地或是歼灭敌人。通常攻城战是不得已的情况下才要进行的战争模式，因为往往需要付出巨大的代价才能达成目标。在中古时期，城堡是攻城战进攻方的主要对手，往往进攻方需要大量的攻城武器（如投石机、冲车及弩炮等）和大量伤亡，才能进入城门，进行巷战。直到火药与火砲的发明，攻取城堡已容易许多，其防御角色渐渐被要塞所取代。

A siege is a military blockade of a city or fortress with the intent of conquering by attrition or assault. The term derives from sedere, Latin for "to sit". Siege warfare is a form of constant, low-intensity conflict characterized by one party holding a strong, static defensive position. Consequently, an opportunity for negotiation between combatants is not uncommon, as proximity and fluctuating advantage can encourage diplomacy.