Performance monitoring is a critical component of dam safety management, particularly for large hydropower dams. Bakun Dam, the largest concrete face rockfill dam in Southeast Asia, is equipped with an extensive instrumentation system designed to monitor the structural, geotechnical and hydraulic behaviour of the dam throughout its operational life. This paper presents a comprehensive review of the performance monitoring and instrumentation systems implemented at Bakun Dam and evaluates their effectiveness in supporting dam safety decision-making.  Long-term monitoring data are examined to assess key safety-related parameters such as reservoir water levels, seepage behaviour, pore water pressure, deformation, rainfall and operational loading conditions. The interpretation of instrumentation data is discussed with respect to identifying normal versus abnormal performance and detecting early warning signs of potential safety issues. The findings demonstrate that a well-designed and properly maintained instrumentation system is essential for understanding dam performance and ensuring long-term safety. The experience from Bakun Dam provides valuable insights for dam owners, operators and regulators involved in dam safety management of large dams worldwide.