Six out of ten completely sequenced bacterial genomes are pathogenic or opportunistic bacteria. The genome sequence of at least one strain of all the principal pathogenic bacteria will soon be available. This information should enable us to identify genes that encode virulence factors. As these genes are potential targets for drugs and vaccines, their identification should have considerable repercussions on prevention, diagnosis, and treatment of the main bacterial infectious diseases. Comparison of genome sequences of several strains of the same species should allow identification of the genetic clues responsible for the differing behavior of related bacterial pathogens. This article reviews the genomes from pathogenic bacteria that have been or are currently being sequenced, describes the main tasks to be accomplished after a genome sequence becomes available, and discusses the benefits of having the genome sequence of bacterial pathogens.