An Information Security Management System (ISMS) is the structured framework an organisation uses to manage security policies, roles, risks, and controls. It is not a single product or checklist; it is the operating model that defines what must be protected, who is responsible, how risks are treated, and how decisions are reviewed. In standards such as ISO 27001, the ISMS is the core object being built, maintained, and audited.
An effective ISMS matters because attacks often exploit weak governance as much as weak technology. If access reviews, patching, logging, vendor checks, or incident response ownership are unclear, controls drift and gaps appear. In defense, an ISMS helps teams keep evidence, assign accountability, and measure whether controls still match the real environment. In attacks, defenders often discover the absence of an ISMS through inconsistent procedures, missing records, or untested recovery steps.