This report, commissioned by the Korean Ministry of Trade Industry and Energy and written jointly by the International Energy Agency and the Korea Energy Economics Institute, examines current conditions and future opportunities to ensure electricity security and system flexibility with higher shares of variable renewable energy in Korea. The report examines the objectives from the 9th Basic Plan for Long-term Electricity (BPLE) in terms of energy demand and variable renewable energy deployment, and provides options to maintain the country’s current high level of electricity security, while integrating increasing shares of solar PV and wind. Taking into consideration the existing institutional and market structure, the analysis first looks into how flexibility needs may evolve in Korea’s power system and suggests technical options to satisfy these requirements making use of flexible generation, storage, demand-side flexibility and grids. The report then looks at key aspects of operational security and long-term planning, both recognising current progress in terms of grid and market code updates as well as suggesting improvements to the long-term planning process, through for example integrated resource planning. The report suggests market design improvements that can be implemented within the current framework, considering price formation mechanisms and integration with the existing emissions trading scheme. Finally, the report examines key aspects of climate and cyber resilience, suggesting improvements that can be integrated into long-term planning to ensure resilience across the whole value chain.