Reactome is an open-source, curated and peer-reviewed pathway database that provides an integrated view of cellular pathways, biological processes, and molecular interactions. It was initiated in 2003 to capture human biological pathways and has since expanded to include other organisms, such as mouse, rat, fruit fly, and worm. Reactome data is manually curated by a team of biologists, who review and annotate published scientific literature to extract information about pathways, biological processes, and molecular interactions. The database contains more than 12,000 reactions and 2,000 pathways, and covers a broad range of biological processes, such as metabolism, signaling, immune system, cell cycle, and DNA repair. Reactome also offers a suite of tools and resources to visualize, analyze, and interpret pathway data. It is widely used by researchers and bioinformaticians to explore and understand biological processes and disease mechanisms.