Gram-negative bacterial foodborne pathogens are a worldwide cause of morbidity and mortality. The ability to carry out epidemiological investigations to determine the primary sources of bacterial contamination is important to improve public health. Multiple methods are available for bacterial source tracking and to determine the distribution of pathogens isolated from sick patients. The molecular based typing methods available fall into three general categories: those based on restriction analysis of the bacterial DNA; those based on polymerase chain reaction (PCR) amplification of particular genetic targets; and those based on the identification of DNA sequence polymorphisms. The techniques that are examined in this review include: plasmid analysis, restriction fragment length polymorphism methods, pulsed-field gel electrophoresis, amplified fragment length polymorphism analysis, PCR-based genotyping, variable number of tandem repeat analysis, multilocus sequence typing, and single nucleotide polymorphism analysis. These methods are described along with a discussion of the strengths and weaknesses of the techniques for genotyping the major Gram-negative foodborne pathogens--Campylobacter spp., Salmonella enterica, Shigella spp., Escherichia coli, and Yersinia enterocolitica.