These thesis explores the topic of after-sales logistics with the objective of analyzing how spare parts planning can contribute to improving service level and creating value along the supply chain. The work stems from the internship experience at Accenture Consulting, in a project aimed at optimizing the planning and inventory management processes for a major automotive manufacturer, and therefore combines a theoretical approach with a practical application in a real industrial context. The first part delves into the concept of service level as a competitive lever, presenting the main performance indicators (Fill Rate, Lead Time, Backorder and OTIF) and discussing their implications in measuring operational effectiveness.