The MEROPS database, maintained by the Wellcome Trust Sanger Institute, is a comprehensive resource for peptidases, their inhibitors, and substrates. It features a hierarchical classification system that groups peptidases and inhibitors into protein species, families, and clans. The database emphasizes distinguishing peptidases through their specific cleavage sites and interactions with inhibitors. Over 39,000 known cleavage sites in proteins, peptides, and synthetic substrates are cataloged, allowing for the display of peptidase specificity and substrate alignments to assess conservation and physiological relevance. The database has seen significant growth in the number of complete genomes, enabling the analysis of peptidase gene gains and losses. New features include interactive dendrograms, enhanced domain architectures, and tools for dynamic substrate alignments. The MEROPS database also includes cross-references to other databases and a distributed annotation system (DAS) for direct data extraction. User contributions are encouraged through a submission feature, and the database is regularly updated to reflect new data and improvements.The MEROPS database, maintained by the Wellcome Trust Sanger Institute, is a comprehensive resource for peptidases, their inhibitors, and substrates. It features a hierarchical classification system that groups peptidases and inhibitors into protein species, families, and clans. The database emphasizes distinguishing peptidases through their specific cleavage sites and interactions with inhibitors. Over 39,000 known cleavage sites in proteins, peptides, and synthetic substrates are cataloged, allowing for the display of peptidase specificity and substrate alignments to assess conservation and physiological relevance. The database has seen significant growth in the number of complete genomes, enabling the analysis of peptidase gene gains and losses. New features include interactive dendrograms, enhanced domain architectures, and tools for dynamic substrate alignments. The MEROPS database also includes cross-references to other databases and a distributed annotation system (DAS) for direct data extraction. User contributions are encouraged through a submission feature, and the database is regularly updated to reflect new data and improvements.