Extraradicular Pathogenesis is a theoretical framework in endodontic microbiology that explains the mechanisms by which microbial agents and their byproducts initiate and perpetuate persistent periapical inflammation and tissue destruction beyond the root canal system, distinguishing itself from intraradicular infection processes by its focus on external root surface colonization, biofilm formation in the peri-radicular environment, and host immune response modulation in the absence of direct pulpal communication.