The TAU parallel performance system is a robust, flexible, and portable framework for performance instrumentation, measurement, analysis, and visualization of large-scale parallel computer systems and applications. Developed over fourteen years, it supports diverse performance observation and analysis requirements. The system is designed as a tool framework with three layers: instrumentation, measurement, and analysis. The instrumentation layer defines performance events, while the measurement layer manages event processing and provides profiling and tracing capabilities. The analysis layer includes tools for visualizing performance data. TAU supports various instrumentation methods, including source-based, preprocessor-based, compiler-based, wrapper library-based, binary instrumentation, interpreter-based, component-based, and virtual machine-based approaches. These methods allow for flexible and efficient performance measurement across different programming languages and environments. The system provides a flexible measurement infrastructure that enables users to experiment with different attributes of the system and iteratively refine performance characterization. TAU's measurement system supports multiple sources of performance data, including time, hardware counters, and system-accessible performance data. It allows for profiling and tracing, with profiling focusing on aggregate performance metrics and tracing providing detailed event information. TAU's profiling system supports flat profiling, callpath profiling, and other variants, enabling detailed analysis of performance events. The system is highly robust, scalable, and has been ported to all HPC platforms. It provides a common interface for performance data, allowing external tools to access the data. TAU's selective instrumentation mechanism allows users to configure which events to instrument, helping to reduce measurement overhead and improve performance analysis. The system also supports multi-level instrumentation, enabling performance data to be collected from multiple levels of the program transformation process. TAU's component-based instrumentation allows for the creation of proxy components that can be used to measure and record performance-related data. The system also supports virtual machine-based instrumentation, enabling performance measurement in Java applications. TAU's measurement system is highly configurable, allowing users to select the performance data to capture and the manner in which it is captured. The system is designed to be flexible and adaptable to different performance requirements and environments.The TAU parallel performance system is a robust, flexible, and portable framework for performance instrumentation, measurement, analysis, and visualization of large-scale parallel computer systems and applications. Developed over fourteen years, it supports diverse performance observation and analysis requirements. The system is designed as a tool framework with three layers: instrumentation, measurement, and analysis. The instrumentation layer defines performance events, while the measurement layer manages event processing and provides profiling and tracing capabilities. The analysis layer includes tools for visualizing performance data. TAU supports various instrumentation methods, including source-based, preprocessor-based, compiler-based, wrapper library-based, binary instrumentation, interpreter-based, component-based, and virtual machine-based approaches. These methods allow for flexible and efficient performance measurement across different programming languages and environments. The system provides a flexible measurement infrastructure that enables users to experiment with different attributes of the system and iteratively refine performance characterization. TAU's measurement system supports multiple sources of performance data, including time, hardware counters, and system-accessible performance data. It allows for profiling and tracing, with profiling focusing on aggregate performance metrics and tracing providing detailed event information. TAU's profiling system supports flat profiling, callpath profiling, and other variants, enabling detailed analysis of performance events. The system is highly robust, scalable, and has been ported to all HPC platforms. It provides a common interface for performance data, allowing external tools to access the data. TAU's selective instrumentation mechanism allows users to configure which events to instrument, helping to reduce measurement overhead and improve performance analysis. The system also supports multi-level instrumentation, enabling performance data to be collected from multiple levels of the program transformation process. TAU's component-based instrumentation allows for the creation of proxy components that can be used to measure and record performance-related data. The system also supports virtual machine-based instrumentation, enabling performance measurement in Java applications. TAU's measurement system is highly configurable, allowing users to select the performance data to capture and the manner in which it is captured. The system is designed to be flexible and adaptable to different performance requirements and environments.