Pigs are susceptible to a wide range of diseases that can affect health, welfare and productivity. The implementation of biosecurity measures along the production chain is one of the major solutions to minimize the risk of introduction of diseases into a farm (external biosecurity), as well as their spread within the farm (internal biosecurity). In this chapter, we discuss the five principles of farm-level biosecurity and illustrate the application of these principles both for external biosecurity (purchasing and quarantine policy, the transport of animals and removal of manure and carcasses, the supply of feed, water, and equipment, the access of persons, vermin and bird control, environmental risks) and for internal biosecurity (compartmentalization, working lines, and equipment, disease management, farrowing and suckling period, weaning and fattening period, and cleaning and disinfection). Finally, ways to measure and quantify the biosecurity status of a pig farm are discussed.