SUMMARYThe EBI Complex Portal is a manually curated, unifying resource of macromolecular complexes from model organisms.Each entry has a unique and stable identifier and links participating molecule to their unique reference database (UniProt, ChEBI and RNAcentral). Each complex is annotated with information about their stoichiometry, topology and structural assembly, function, complex-centric Gene Ontology terms and evidence codes. Complexes are extensively cross-referenced to ChEMBL, EMDB, Experimental Factor Ontology, Intenz, MatrixDB, the PDB and Reactome. Bespoke visualisation tools for the general topology and stoichiometry, crystal structures, molecular reactions and gene expression data are provided. All data is open-source and available in PSI-MI xml2.5 and xml3.0 standard formats, MI-JSON and tab-delineated ComplexTAB format.