纵深防御是为一种军事战略，有时也称作弹性防御或是深层防御，是以全面深入的防御去延迟而不是阻止前进中的敌人，透过放弃空间来换取时间与给予敌人额外的伤亡。有别于以一个单一而强大的防御战线去防御敌人，纵深防御试图用下列方式阻击敌人

对防御者而言，他会放弃在领土上相对微弱的抵抗，而采取全力压迫攻击方之后勤补给，或是切割敌方在数量上的优势的兵力。一但攻击方失去其动能，或是其在大部份地区被切割后的兵力数量优势不再，防御反攻将在敌人虚弱地带发动，其主旨在于促使敌方资源之消耗，进而带动消耗战，或是迫使攻击方退回原本攻击起始点。 纵深防御的概念如今也广泛的用于解释一些非军事的决策上。

Defence in depth (also known as deep or elastic defence) is a military strategy that seeks to delay rather than prevent the advance of an attacker, buying time and causing additional casualties by yielding space. Rather than defeating an attacker with a single, strong defensive line, defence in depth relies on the tendency of an attack to lose momentum over time or as it covers a larger area. A defender can thus yield lightly defended territory in an effort to stress an attacker's logistics or spread out a numerically superior attacking force. Once an attacker has lost momentum or is forced to spread out to pacify a large area, defensive counter-attacks can be mounted on the attacker's weak points, with the goal being to cause attrition warfare or drive the attacker back to its original starting position.