# Defense in Depth

A security strategy that layers multiple independent defenses so that no single failure leaves a system fully exposed.

**Defense in depth[↗](/defense-in-depth)** is a security strategy built on layering multiple, independent defenses, firewalls, endpoint[↗](/endpoint) protection, network segmentation[↗](/network-segmentation), strong authentication[↗](/authentication), and employee training, so that if one layer fails or is bypassed, others are still in place to catch the threat. It rejects the idea that any single control can be relied on to stop everything.

The concept borrows from military strategy, where a single defensive line is riskier than several successive ones. In practice, this means an organization shouldn't rely solely on a firewall[↗](/firewall), for instance, but should combine it with monitoring, access controls, and backups so that a determined attacker faces obstacles at every stage.