Abstract This chapter gives an overview of different methods for improving surface properties of plastics. Plastics are inherently hydrophobic, low surface energy materials and thus do not adhere well to other materials. Adhesion improvement is the most common application but other surface characteristics, such as wettability, water- and chemical resistance, nonfouling, tribological behavior, oxygen, and moisture transmission are also addressed. It has been estimated that 70% of the total production of plastic materials must be surface treated prior to processing. The methods range from vacuum to atmospheric pressure, wet to dry, simple to sophisticated, and inexpensive to very costly to obtain the required functional characteristics of plastics. Most methods used today are dry and environmentally sound. The methods presented are roughly divided in surface activation (e.g., plasma, corona, flame, and UV laser) and surface coating (e.g., plasma polymerization, chemical vapor deposition, Parylene, physical vapor deposition) techniques.