KEGG (Kyoto Encyclopedia of Genes and Genomes) is a comprehensive database that integrates genomic, chemical, and systemic functional information to link genomes to life and the environment. It provides a reference knowledge base for understanding cellular processes and organism behaviors through pathway mapping and BRITE mapping. KEGG PATHWAY, a key component, has been expanded with a new global metabolic pathway map and smaller pathway modules stored in KEGG MODULE. KEGG BRITE, an ontology database, represents functional hierarchies of various biological objects, including molecules, cells, organisms, diseases, and drugs. KEGG DRUG contains all approved drugs in the US and Japan, while KEGG DISEASE links disease genes, pathways, drugs, and diagnostic markers. The KEGG resource is highly integrated, with 19 databases categorized into systems information, genomic information, and chemical information. Genome annotation assigns KEGG Orthology (KO) identifiers to genes, facilitating the linking of genomes to biological systems. Chemical annotation links genomic or transcriptomic content to chemical structures, and KEGG REACTION and KEGG RPAIR characterize the chemical transformations in enzymatic reactions. KEGG is accessible via the Japanese GenomeNet service and a new website, with ongoing efforts to enhance its utility in medical, pharmaceutical, and environmental sciences.KEGG (Kyoto Encyclopedia of Genes and Genomes) is a comprehensive database that integrates genomic, chemical, and systemic functional information to link genomes to life and the environment. It provides a reference knowledge base for understanding cellular processes and organism behaviors through pathway mapping and BRITE mapping. KEGG PATHWAY, a key component, has been expanded with a new global metabolic pathway map and smaller pathway modules stored in KEGG MODULE. KEGG BRITE, an ontology database, represents functional hierarchies of various biological objects, including molecules, cells, organisms, diseases, and drugs. KEGG DRUG contains all approved drugs in the US and Japan, while KEGG DISEASE links disease genes, pathways, drugs, and diagnostic markers. The KEGG resource is highly integrated, with 19 databases categorized into systems information, genomic information, and chemical information. Genome annotation assigns KEGG Orthology (KO) identifiers to genes, facilitating the linking of genomes to biological systems. Chemical annotation links genomic or transcriptomic content to chemical structures, and KEGG REACTION and KEGG RPAIR characterize the chemical transformations in enzymatic reactions. KEGG is accessible via the Japanese GenomeNet service and a new website, with ongoing efforts to enhance its utility in medical, pharmaceutical, and environmental sciences.