Airless and air-assisted high-pressure spray guns are widely used in the spray painting industry. The present contribution summarizes ongoing investigations on the spray painting processes of these two atomizers using real paint material. Atomization processes under airless and air-assisted conditions were experimentally studied by measuring droplet size distributions and droplet velocities using a Spraytec Fraunhofer-type particle sizer and laser-Doppler anemometry. A computational fluid dynamics code was applied to calculate the flow field and the droplet trajectories. The measured and calculated film thickness distributions on the substrate were compared. The experimental and simulation results provided the necessary information for understanding the painting process using airless and air-assisted systems and for improving the performance of these atomizers.