Continuous monitoring activities include configuration management and control of information system components, security impact analyses of changes to the system, ongoing assessment of security controls, and status reporting. The organization assesses all security controls in an information system during the initial security accreditation. Subsequent to the initial accreditation and in accordance with OMB policy, the organization assesses a subset of the controls annually during continuous monitoring. The selection of an appropriate subset of security controls is based on: (i) the FIPS 199 security categorization of the information system; (ii) the specific security controls selected and employed by the organization to protect the information system; and (iii) the level of assurance (or grounds for confidence) that the organization must have in determining the effectiveness of the security controls in the information system. The organization establishes the selection criteria and subsequently selects a subset of the security controls employed within the information system for assessment. The organization also establishes the schedule for control monitoring to ensure adequate coverage is achieved. Those security controls that are volatile or critical to protecting the information system are assessed at least annually. All other controls are assessed at least once during the information system’s three- year accreditation cycle. The organization can use the current year’s assessment results obtained during continuous monitoring to meet the annual FISMA assessment requirement (see CA-2). This control is closely related to and mutually supportive of the activities required in monitoring configuration changes to the information system. An effective continuous monitoring program results in ongoing updates to the information system security plan, the security assessment report, and the plan of action and milestones—the three principle documents in the security accreditation package. A rigorous and well executed continuous monitoring process significantly reduces the level of effort required for the reaccreditation of the information system. NIST Special Publication 800-37 provides guidance on the continuous monitoring process. NIST Special Publication 800-53A provides guidance on the assessment of security controls. Related security controls: CA-2, CA-4, CA-5, CA-6, CM-4.