This chapter discusses the manufacturing tool Key efficiency indicator (KPI). It began by reviewing the definitions and concepts of the primary research carried out on the reported tool to explain the implementation process and the benefits its application brings to organizations. A case study was conducted to increase the efficiency KPI of the assembly line of a German automotive electrical harness company, where the state of the production line was determined with lean tools such as the CTQ diagram (Critical Quality Parameters), the SIPOC diagram (Supplier Inputs Process Outputs Customers), and the Value Stream Graph (VSM), which together with the process metrics, showed a real panorama of the line. To analyze the root cause, the factors that intervene, and based on the results, the techniques applied to solve the causes that generate the lack of compliance with the efficiency KPI were determined. The average uptime of the line before the improvements was 1245 min per day, and with the implementation of the lean tools, it increased to 1350 productive minutes per day, demonstrating a significant efficiency increase in the line of 8% of productive minutes per day.