The stability, productivity, sustainability and profitability of the global swine industry depend upon many factors and conditions, including infectious diseases. These diseases have a significant impact on animal health worldwide, and in some instances upon human health due to their zoonotic impact. This chapter discusses the basic features of swine viruses, including aspects of pathogenesis and transmission mechanisms. In certain instances, clinical signs caused by swine viruses are not specific enough to establish a sound clinical and/or pathological diagnosis, and laboratory investigations are required to ascertain which virus or viruses are causing disease. A summary of the most frequent clinical signs, lesions and diagnostic methods for relevant swine viral infections will be described. The chapter concludes with commonly used measures for the prevention and control of viral pig diseases, emphasizing the importance of vaccination as the cornerstone of swine health programmes.