CISO-as-a-Service, also known as virtual CISO (vCISO), is a service model in which organizations engage an experienced security executive on a fractional, subscription, or on-demand basis rather than hiring a full-time Chief Information Security Officer. These engagements deliver strategic security leadership—defining security strategy, building risk management programs, overseeing compliance efforts, and advising executive leadership and boards—without the cost of a permanent hire. Core deliverables typically include security program development, policy and governance frameworks, risk assessments, roadmap planning, and regulatory or audit readiness for standards such as SOC 2, ISO 27001, HIPAA, and PCI DSS. Providers often supply a team of practitioners backed by established methodologies, giving smaller and mid-sized organizations access to enterprise-grade expertise. The model is especially valuable for companies that must satisfy customer or regulatory security requirements but lack the scale to justify a dedicated executive, as well as for organizations in transition, seeking interim leadership, or needing specialized guidance for a specific initiative. Engagement models range from advisory-only arrangements to hands-on program management, allowing organizations to match the depth of leadership to their maturity and budget.