Simulation and virtual commissioning are critical enablers for achieving the goals of Industry 4.0 and5.0 by allowing safe, efficient testing and optimization of production systems. This thesis, conducted incollaboration with Scania Oskarshamn, explores the use of Siemens SIMIT to improve the commissioningprocess and evaluate the potential transition toward digital twins. The results show that virtual com-missioning can reduce commissioning time and costs. For a single project, the consultant-based approachnearly breaks even with a gain of about 6 000 SEK, while the internal approach achieves around 48 000 SEK.Costs decrease further when license fees are distributed over more projects and as experience and reusableSIMIT components reduce effort. In addition to the financial impact, virtual commissioning improvesdeadline control, reduces downtime, and enhances risk management. The study highlights that SIMIT,particularly with the FLOWNET library, is effective for simulating subsystems like ventilation and paintshops, offering a valuable way to validate and compare solutions. However, realistic simulation of objectmovement often requires integration with tools such as RobotStudio, as the CONTEC library alone is lessaccurate for discrete manufacturing applications.