Publisher Summary This chapter describes what is vulnerability assessment, what it can provide, and why one should be performing them as often as possible. Vulnerability refers to any programming error or misconfiguration that could allow an intruder to gain unauthorized access. This includes anything from a weak password on a router to an unpatched programming flaw in an exposed network service. Vulnerabilities are no longer the realm of just system crackers and security consultants and have become the enabling factor behind most network worms, spyware applications, and e-mail viruses. Vulnerability assessments have become the preferred method of managing security flaws for many organizations. The ability to quickly identify misconfigured and unpatched systems, combined with the ease of use and accuracy of many assessment tools, has changed the way many administrators manage their systems. Network vulnerability assessments provide the wide view of security weaknesses on a given network, supplemented by host assessment solutions that provide granular hardening steps for critical systems. The traditional process of system hardening and patch application has been left in the dust; the sheer quantity of vulnerabilities is more than any administrator can keep track of, especially for diverse networks. Automated assessment solutions have come to the rescue, with both stand-alone and subscription-based options. The average administrator no longer needs to become a security savant simply to keep his or her systems secure. The same repeatable process allows administrators to track, resolve, and verify vulnerabilities.