Essential genes are frequently conserved among bacterial species and thus microbial and eukaryote genome comparisons can be used to compile datasets of homologous proteins and families that can be utilized to identify attractive targets for the design of antimicrobial agents and other drugs. These searches can now often be conducted using Web tools. A number of such resources that provide sequence information and comparative software as well as computational tools for convenient analysis of the data are summarized here and their step-by-step use explained.