Reactome is a comprehensive, expert-authored, peer-reviewed knowledgebase of human biological pathways and processes, serving as both a data mining resource and an electronic textbook. The current release includes 2975 human proteins, 2907 reactions, and 4455 literature citations. Key features include a new entity-level pathway viewer, improved search and data mining tools, and enhanced orthology prediction methods for 22 species. Reactome has expanded its utility to model organisms, with curated datasets for Arabidopsis, rice, Drosophila, and chicken. The knowledgebase supports data integration and user support through various tools and formats, including SBML, Protégé, Cytoscape, and BioPax. Future developments aim to provide intuitive graphical representations of pathways and reactions, with ongoing work on an entity-level pathway visualization tool and a new author tool for creating textbook-style illustrations.Reactome is a comprehensive, expert-authored, peer-reviewed knowledgebase of human biological pathways and processes, serving as both a data mining resource and an electronic textbook. The current release includes 2975 human proteins, 2907 reactions, and 4455 literature citations. Key features include a new entity-level pathway viewer, improved search and data mining tools, and enhanced orthology prediction methods for 22 species. Reactome has expanded its utility to model organisms, with curated datasets for Arabidopsis, rice, Drosophila, and chicken. The knowledgebase supports data integration and user support through various tools and formats, including SBML, Protégé, Cytoscape, and BioPax. Future developments aim to provide intuitive graphical representations of pathways and reactions, with ongoing work on an entity-level pathway visualization tool and a new author tool for creating textbook-style illustrations.