Many lines of evidence link antimicrobial-resistant human infections to foodborne pathogens of animal origin. Types of evidence reviewed include: (1) direct epidemiologic studies; (2) temporal evidence; (3) additional circumstantial evidence; (4) trends in antimicrobial resistance among Salmonella isolates; and (5) trends in antimicrobial resistance among other pathogens, such as Campylobacter jejuni. Commensal microorganisms in animals and humans may contribute to antimicrobial resistance among pathogens that cause disease among humans. For instance, enterococci of food-animal origin, particularly strains that are vancomycin resistant, have been linked to strains found in the human gastrointestinal tract. The latent period between the introduction of a given antimicrobial and emergence of resistance varies considerably, but once the prevalence in a population reaches a certain level, control becomes extremely difficult.