Infections with bacterial pathogens have a significant impact on the health, well-being and performance of pigs worldwide. Infections are responsible for antimicrobial use, and therefore, increase the risk for the development of antimicrobial resistance. Some bacterial pathogens in swine are also important zoonotic agents. The present chapter discusses classical phenotypic characteristics as well as more advanced molecular techniques to identify and classify bacteria. Bacterial pathogens can express a wide range of virulence, and may cause disease by different mechanisms such as tissue invasion and toxin production. Transmission can take place by many different routes. Direct contact occurs for all bacterial pathogens, whereas indirect transmission may vary depending on the pathogen. Clinical signs and lesions caused by the most important swine bacterial pathogens, as well as approaches to establish a diagnosis are summarized. The chapter ends with discussing commonly used measures for prevention and control, including strengths and weaknesses of vaccination.