This study investigates how different process gases (air, argon, and nitrogen) influence the wettability and adhesive bond strength of DC01 steel and polypropylene surfaces treated by laser and plasma methods. The aim was to clarify how gas composition and processing parameters affect surface activation and whether contact angle measurements alone can explain adhesive performance. On DC01 steel, laser treatment significantly reduced water contact angles, achieving full wetting at specific power and scanning speeds. However, lap shear testing showed that a 0° contact angle did not always result in the same bond strengths. Argon-treated samples consistently provided the highest shear strength. For polypropylene, plasma activation improved both wettability and bonding. Nitrogen plasma lowered contact angles from 63° on untreated surfaces to 14° at 200 mm/min and 9° at 400 mm/min, producing the strongest joints. This study is one of the first to systematically compare the effects of different gases on metals and polymers, linking wettability and mechanical testing to offer practical guidance for optimizing process parameters for strong and reliable adhesive joints.