Security strategy using multiple layers of controls so that if one fails, others provide protection.
Defence in depth is a security strategy employing multiple layers of controls—so if one layer fails, others continue to provide protection. Rather than relying on a single control, defence in depth combines perimeter security, network segmentation, endpoint protection, access controls, monitoring, and user awareness. This layered approach means attackers must overcome multiple barriers, increasing detection opportunities and limiting the impact of any single control failure.