Abstract: The interactions between bacterial pathogens and their hosts is complex. To further our understanding of　the pathogenesis　of bacterial pathogens, it is necessary to identify bacterial virulence genes that are specifically induced in vivo during infection and probe their regulation in vivo. Toward this end, several technologies, such as in vivo expression technology (IVET), signature-tagged mutagenesis (STM), differential fluorescence induction (DFI), genomic analysis and mapping by in vitro transposition (GAMBIT) and in vivo induced antigen technology (IVIAT), have been developed. The purpose of this review　is to update the reader on the many advances of these technologies, and to discuss their advantages and disadvantages.