The next stage of genome sequencing projects will be a proteome analysis stage. The proteome means a set of all proteins in a living cell, and studies about the proteome or genome-scale protein analyses are called "proteomics". Many proteins do not work by themselves in vivo, but, in most cases, work by forming a complex or interacting with other proteins, DNA, RNA, or ligands (interactome). In our laboratory, comprehensive identification of protein interactions is now in progress by using originally developed methods, in vitro virus and STABLE in which protein(phenotype) is physically linked into its encoding mRNA/DNA(genotype). In vitro virus and STABLE methods are high-throughput and powerful tools for screening of protein interactions.