This chapter explores causal attribution as a fundamental concept in impact assessment, examining its theoretical foundations and practical applications in educational assessment. It defines causal attribution as determining if changes are due to a specific intervention rather than external factors. Drawing from psychology and social sciences, it covers its history, challenges, and significance. It discusses challenges such as creating valid comparison groups, controlling external variables, and addressing ethical considerations, and it offers strategies to address these challenges. The chapter reviews major theoretical and methodological approaches, with examples. It advocates for a systemic view, viewing causal attribution as a valuable tool for understanding change, improving program design, and decision-making through evidence. It emphasizes the importance of distinguishing between correlation and causation, ensuring that evaluations are statistically sound and relevant.