This chapter, titled "On-the-Job Training: Costs, Returns, and Some Implications," by Jacob Mincer, explores the economic aspects of on-the-job training (OJT) as a form of human capital investment. Mincer emphasizes that formal education is not the sole method of training, and OJT, which includes both formal and informal learning, is crucial for acquiring occupational skills. He estimates the costs of OJT, which are primarily opportunity costs of foregone earnings, and discusses the challenges in accurately measuring these costs due to data limitations and conceptual issues. Mincer also examines the rates of return on OJT, using specific examples such as apprenticeship training, and compares them with the rates of return on formal education. He concludes that OJT is a significant investment, particularly at higher educational levels, and that its costs and returns are influenced by various factors, including age, gender, and occupation. The chapter provides insights into the economic behavior of individuals and firms in the context of human capital investment.This chapter, titled "On-the-Job Training: Costs, Returns, and Some Implications," by Jacob Mincer, explores the economic aspects of on-the-job training (OJT) as a form of human capital investment. Mincer emphasizes that formal education is not the sole method of training, and OJT, which includes both formal and informal learning, is crucial for acquiring occupational skills. He estimates the costs of OJT, which are primarily opportunity costs of foregone earnings, and discusses the challenges in accurately measuring these costs due to data limitations and conceptual issues. Mincer also examines the rates of return on OJT, using specific examples such as apprenticeship training, and compares them with the rates of return on formal education. He concludes that OJT is a significant investment, particularly at higher educational levels, and that its costs and returns are influenced by various factors, including age, gender, and occupation. The chapter provides insights into the economic behavior of individuals and firms in the context of human capital investment.