The main activity of Marel is the design and production of food processing lines. It creates additional value to its products by offering valuable services to customers. One of these services is the critical parts package. This package contains all the service parts that may fail suddenly and that are critical for the customers. Marel wants to offer its customers the best package in terms of achieved service levels and investment costs. Roel Bongers conducted a master thesis project that focused on improving the concepts used to determine optimal spare part inventory levels and to create the critical parts package.