This book discusses the application of the coupled CFD-DEM approach for simulating the separation of grain and material other than grain in combine harvester cleaning devices. Based on a literature study, it describes the most important influencing factors and presents a database for particle parameterization. It investigates the separation process in two steps with differing levels of process abstraction. The first step involves numerical separation in a vertically oscillating box with airflow, and in the context of a sensitivity study, investigates the effect of selected material, contact and operating parameters on the target variables’ separation time and grain purity. In the second step, the numerical separation process was performed in a 200 mm wide segment of a combine harvester cleaning device. The numerical results were then compared with experimental investigations in order to confirm the method applicability.