This lecture introduces the concept of cost benefit analysis using examples from the transportation industry, such as the evaluation of buying a new aircraft for an airline or the construction of the Gotthard base tunnel. It covers the methodology, stakeholders involved, different types of indicators (monetary and non-monetary), and the challenges of estimating costs and benefits accurately. The lecture also discusses the transformation of non-monetary aspects into monetary units, the importance of multi-criteria analysis, and the implications of subjectivity in decision-making processes.