The rapid electrification of transportation has transformed electric vehicles from passive loads into potentially active components of power systems. Among the most promising paradigms emerging from this transformation is Vehicle-to-Grid (V2G) integration, which enables bidirectional power flows between electric vehicles and the electricity grid. This research article presents an extensive, theory-driven, and system-level analysis of V2G integration, focusing on its implications for frequency regulation, renewable energy integration, grid stability, and market structures. Drawing strictly from the provided body of scholarly references, the study synthesizes insights from empirical case studies, optimization-based scheduling models, profitability analyses under uncertainty, and comprehensive electric vehicle modeling frameworks. Particular attention is given to the role of V2G in high-renewable systems, such as wind-dominant and solar-integrated grids, and to its applicability across diverse national contexts, including Colombia, Denmark, and emerging economies in Southeast Asia. The methodology relies on qualitative comparative analysis and conceptual modeling grounded in the reviewed literature, avoiding mathematical formalism while providing detailed explanatory narratives of optimization logic, uncertainty handling, and system interactions. The results demonstrate that V2G can significantly enhance frequency regulation performance, reduce renewable curtailment, and create new value streams for electric vehicle owners and aggregators, albeit with nontrivial challenges related to battery degradation, user behavior, regulatory uncertainty, and market design. The discussion critically examines these challenges, explores counter-arguments regarding scalability and equity, and outlines future research directions centered on artificial intelligence–driven scheduling, vehicle aggregation, and integrated energy system planning. The article concludes that V2G should be understood not merely as a technical add-on but as a structural element of future smart grids, requiring coordinated advances in technology, policy, and socio-economic frameworks.