CORUM is a comprehensive database that provides a manually curated repository of experimentally characterized protein complexes from mammalian organisms, primarily human (64%), mouse (16%), and rat (12%). The new CORUM 2.0 release includes 2837 protein complexes, making it the largest and most extensive publicly available dataset of mammalian protein complexes. Each complex is described with its name, subunit composition, function, and literature references. Recent developments include mapping functional annotations to Gene Ontology terms and cross-references to Entrez Gene identifiers. A new 'Phylogenetic Conservation' tool allows users to predict the occurrence of orthologous protein complex subunits in different phylogenetic groups, aiding in the analysis of protein complex evolution. The dataset is freely accessible at http://mips.helmholtz-muenchen.de/gene/proj/corum/index.html.CORUM is a comprehensive database that provides a manually curated repository of experimentally characterized protein complexes from mammalian organisms, primarily human (64%), mouse (16%), and rat (12%). The new CORUM 2.0 release includes 2837 protein complexes, making it the largest and most extensive publicly available dataset of mammalian protein complexes. Each complex is described with its name, subunit composition, function, and literature references. Recent developments include mapping functional annotations to Gene Ontology terms and cross-references to Entrez Gene identifiers. A new 'Phylogenetic Conservation' tool allows users to predict the occurrence of orthologous protein complex subunits in different phylogenetic groups, aiding in the analysis of protein complex evolution. The dataset is freely accessible at http://mips.helmholtz-muenchen.de/gene/proj/corum/index.html.