The RACI Matrix (Responsibility Assignment Matrix) is a project management framework that clarifies task ownership by mapping each activity to exactly four roles: Responsible, Accountable, Consulted, and Informed. Originating in project management practice and later formalized in frameworks like PMBOK, RACI solves the accountability ambiguity that plagues cross-functional teams by answering two critical questions: who does the work, and who owns the outcome. The golden rule is simple but non-negotiable: every task needs exactly one Accountable owner—multiple accountables create diffusion of responsibility, while no accountable means work falls through cracks. When properly implemented, RACI transforms vague "someone should handle this" conversations into clear ownership structures with defined communication paths and escalation routes.