PubChem is a public repository for chemical substances and their biological activities, launched in 2004 as part of the NIH's Molecular Libraries Roadmap Initiative. It contains three interlinked databases: Substance, Compound, and BioAssay. The Substance database stores information submitted by contributors, while the Compound database holds unique chemical structures extracted from Substance. The BioAssay database contains biological activity data from assays. PubChem provides tools for data submission, chemical structure standardization, and web-based and programmatic access. It also includes PubChem3D, which provides 3D molecular structures, and PubChemRDF, which offers RDF-formatted data for integration with other databases. PubChem supports various search methods, including text-based searches via Entrez and chemical structure searches. It allows users to download data in multiple formats and provides programmatic access through PUG-REST, PUG-SOAP, and PUG. PubChem continues to evolve, incorporating new tools and services to meet the needs of the scientific community. It serves as a key resource for chemical information, supporting research in areas such as cheminformatics, chemical biology, and drug discovery. PubChem's data are sourced from a wide range of contributors, including universities, government agencies, and pharmaceutical companies, and include a variety of chemical types. The database is continually updated to reflect advances in technology and data integration. PubChem also provides access to regulatory agency data and links to patent information. It supports both text and non-textual searches, and offers tools for data analysis and integration with other databases. PubChemRDF facilitates data sharing and integration with semantic web technologies. Overall, PubChem is a comprehensive resource for chemical information, providing a wide range of tools and services for researchers.PubChem is a public repository for chemical substances and their biological activities, launched in 2004 as part of the NIH's Molecular Libraries Roadmap Initiative. It contains three interlinked databases: Substance, Compound, and BioAssay. The Substance database stores information submitted by contributors, while the Compound database holds unique chemical structures extracted from Substance. The BioAssay database contains biological activity data from assays. PubChem provides tools for data submission, chemical structure standardization, and web-based and programmatic access. It also includes PubChem3D, which provides 3D molecular structures, and PubChemRDF, which offers RDF-formatted data for integration with other databases. PubChem supports various search methods, including text-based searches via Entrez and chemical structure searches. It allows users to download data in multiple formats and provides programmatic access through PUG-REST, PUG-SOAP, and PUG. PubChem continues to evolve, incorporating new tools and services to meet the needs of the scientific community. It serves as a key resource for chemical information, supporting research in areas such as cheminformatics, chemical biology, and drug discovery. PubChem's data are sourced from a wide range of contributors, including universities, government agencies, and pharmaceutical companies, and include a variety of chemical types. The database is continually updated to reflect advances in technology and data integration. PubChem also provides access to regulatory agency data and links to patent information. It supports both text and non-textual searches, and offers tools for data analysis and integration with other databases. PubChemRDF facilitates data sharing and integration with semantic web technologies. Overall, PubChem is a comprehensive resource for chemical information, providing a wide range of tools and services for researchers.