The Human Metabolome Database (HMDB) is the most comprehensive and curated collection of human metabolite and metabolism data worldwide. It contains over 2180 endogenous metabolites with information from thousands of sources. The HMDB includes extensive experimental data from mass spectrometry and NMR analyses, as well as thousands of reference spectra. Each metabolite entry includes over 90 data fields, such as chemical and biological information, disease associations, and links to other databases. The HMDB provides extensive searching, querying, and browsing tools for metabolites, biofluid concentrations, enzymes, genes, spectra, and disease information. It is designed for use by biochemists, clinical chemists, physicians, and others in the metabolomics community. The HMDB is available at www.hmdb.ca. The HMDB is a multi-purpose database combining bioinformatics, cheminformatics, and medical informatics. It integrates data from literature, experimental studies, and databases like KEGG and OMMBID. It includes over 27,700 synonyms, 115 pathways, 2080 enzymes, 110,000 SNPs, and 862 diseases. It also contains over 400 compounds with reference NMR and MS/MS spectra, and 883 compounds with concentration data. The database is searchable and includes tools for structure similarity, sequence similarity, and spectral matching. It also includes a data extraction tool for complex queries and a spectral search utility for identifying compounds from NMR or MS spectra. The HMDB is continuously updated with new data and includes a variety of tools for metabolite identification and analysis. It also includes SimCell models for metabolic pathway simulations. The HMDB is a work in progress, with ongoing additions and corrections. It is expected to grow and evolve, eventually moving from a curated database to a public-deposition model. The HMDB is a comprehensive resource for metabolomics research, providing a wealth of data for researchers, educators, and the general public.The Human Metabolome Database (HMDB) is the most comprehensive and curated collection of human metabolite and metabolism data worldwide. It contains over 2180 endogenous metabolites with information from thousands of sources. The HMDB includes extensive experimental data from mass spectrometry and NMR analyses, as well as thousands of reference spectra. Each metabolite entry includes over 90 data fields, such as chemical and biological information, disease associations, and links to other databases. The HMDB provides extensive searching, querying, and browsing tools for metabolites, biofluid concentrations, enzymes, genes, spectra, and disease information. It is designed for use by biochemists, clinical chemists, physicians, and others in the metabolomics community. The HMDB is available at www.hmdb.ca. The HMDB is a multi-purpose database combining bioinformatics, cheminformatics, and medical informatics. It integrates data from literature, experimental studies, and databases like KEGG and OMMBID. It includes over 27,700 synonyms, 115 pathways, 2080 enzymes, 110,000 SNPs, and 862 diseases. It also contains over 400 compounds with reference NMR and MS/MS spectra, and 883 compounds with concentration data. The database is searchable and includes tools for structure similarity, sequence similarity, and spectral matching. It also includes a data extraction tool for complex queries and a spectral search utility for identifying compounds from NMR or MS spectra. The HMDB is continuously updated with new data and includes a variety of tools for metabolite identification and analysis. It also includes SimCell models for metabolic pathway simulations. The HMDB is a work in progress, with ongoing additions and corrections. It is expected to grow and evolve, eventually moving from a curated database to a public-deposition model. The HMDB is a comprehensive resource for metabolomics research, providing a wealth of data for researchers, educators, and the general public.