The mouse is a key model organism for the understanding of mammalian biology because it has been well studied and is genetically and physiologically similar to humans. To utilize mouse data to its fullest, we have developed an integrated database of mouse genetic, genomic and biological data. The Mouse Genome Informatics Database (MGI) is used by the international scientific community as its primary resource for mouse information and as a tool for new biological discovery. The database contains a wide variety of data pertaining to genes, their DNA and protein sequences, and the phenotypes that result from mutations in different genes. The three central components of MGI are the Mouse Genome Database (MGD), an internationally recognized database for the laboratory mouse, the Mouse Tumor Biology (MTB) database, which facilitates the selection of experimental models for cancer research, and the International Mouse Strain Resource (IMSR), a searchable online database cataloging mouse stocks available worldwide. The database continues to expand to keep abreast of new technologies and to grow with our expanding knowledge of how the genetic blueprint of DNA manifests in traits of a living individual.