This chapter presents a review of the evaluation of prevention programs in the twenty-first century, emphasizing its evolution and importance as an essential component to ensure the efficacy and effectiveness of preventive interventions. The evolution of evaluation approaches is addressed, from summative to more comprehensive methods that include the evaluation of efficacy, effectiveness, impact, and cost-effectiveness. It also discusses current trends in assessment, such as the use of technology, collaborative approaches, and adaptive assessments to respond to cultural and social diversity. A model of evaluation by expectation of results is proposed, which complements conventional approaches by providing a more detailed perspective on the effectiveness of programs and their applicability in varied contexts. Finally, the relationship of evaluation with the guarantee of rights to health and well-being is underlined, and the need for ethical rigor in the evaluation process to avoid misleading or partial results is highlighted.