Book excerpt: The purpose of the National Institute of Standards and Technology Special Publication 800-137 “Information Security Continuous Monitoring (ISCM) for Federal Information Systems and Organizations guideline is to assist organizations in the development of a continuous monitoring strategy and the implementation of a continuous monitoring program providing visibility into organizational assets, awareness of threats and vulnerabilities, and visibility into the effectiveness of deployed security controls. It provides ongoing assurance that planned and implemented security controls are aligned with organizational risk tolerance as well as the information needed to respond to risk in a timely manner should observations indicate that the security controls are inadequate.~