This chapter analyses the central role of evaluation in assessing aid effectiveness, particularly in governance reforms. It reviews OECD evaluation criteria, principles, and methodologies, showing how evaluations enhance accountability and learning while navigating political contexts. Case studies from Ethiopia, Mozambique, and Pakistan illustrate the potential and limitations of external support, revealing both achievements and structural obstacles. Evaluation emerges as a crucial yet inherently interpretive exercise, shaped by negotiation between donors, consultants, and local actors. The chapter argues that rigorous, transparent evaluations are indispensable to improve effectiveness and credibility in development cooperation.