Penetration testing involves evaluating an organization's security by attempting to exploit vulnerabilities from an attacker's perspective. It is comprised of several phases including reconnaissance, network scanning, vulnerability testing, and reporting. Reconnaissance involves gathering open source information on a target, network scanning identifies live hosts and open ports, vulnerability testing checks for known issues and attempts exploitation, and reporting documents the findings and recommendations. Regular penetration testing is recommended or required by certifications and standards to audit security and identify weaknesses.