This chapter consolidates and expands upon performance and evaluation (P&E) concepts introduced throughout the book, presenting a comprehensive framework of foundational principles. It establishes that performance and evaluation are interdependent constructs central to professional practice, connecting previous discussions about comparisons, standards, and judgements to form a coherent theoretical foundation. The chapter articulates three sets of principles: Foundational Principles (FP) that establish the relationship between activities, energy exchange, and outcomes; Performance Principles (PP) that define the scope and requirements of performance measurement; and Evaluation Principles (EP) that address the nature and limitations of performance assessment. Key distinctions are made between unity (individual) and collective performance, physically perceivable versus unperceivable constructs, and quantitative versus qualitative metrics. The framework emphasises that ideal and complete performance concepts require precise metrics, clear units of measurement, contextual understanding, and well-defined evaluation criteria. The chapter particularly highlights the importance of considering context when making comparisons and judgements, acknowledging that evaluations against standards may not be directly transferable across different conditions. Professionals can use this structured approach to develop and apply P&E practices effectively.