This fifth edition of the Common Sense Guide to Mitigating Insider Threats provides the CERT Insider Threat Center’s most current recommendations from the CERT Division, part of Carnegie Mellon University’s Software Engineering Institute. These recommendations are based on our continued research and analysis of an expanded corpus of over 1,000 cases of insider threat. The problem of insider threat impacts organizations across all industries. Although the attack methods vary depending on the industry, the primary types of attacks we have identified—theft of intellectual property, sabotage, fraud, and espionage—continue to hold true. This edition of the Common Sense Guide also considers unintentional insider incidents.