The Conserved Domain Database (CDD) is a comprehensive resource for protein domain annotation, providing multiple sequence alignments and derived database search models that represent conserved protein domains. CDD is accessible via NCBI's Entrez query system and offers precalculated domain annotations for proteins tracked in the Entrez database. It also supports novel protein sequences through the CD-Search service. Starting with version 2.14, CDD summarizes redundant and homologous domain models at the superfamily level, flagging annotations as either 'specific' (high-confidence molecular function) or 'non-specific' (superfamily membership only). CDD clusters domain models into superfamilies to handle redundancy and provides detailed annotations of functional sites, such as catalytic or binding interfaces. The database is regularly updated and can be searched by keyword or protein query sequence, with precalculated annotations updated several times daily. CDD is part of NCBI's Entrez system and is linked to other resources, facilitating comprehensive protein sequence analysis.The Conserved Domain Database (CDD) is a comprehensive resource for protein domain annotation, providing multiple sequence alignments and derived database search models that represent conserved protein domains. CDD is accessible via NCBI's Entrez query system and offers precalculated domain annotations for proteins tracked in the Entrez database. It also supports novel protein sequences through the CD-Search service. Starting with version 2.14, CDD summarizes redundant and homologous domain models at the superfamily level, flagging annotations as either 'specific' (high-confidence molecular function) or 'non-specific' (superfamily membership only). CDD clusters domain models into superfamilies to handle redundancy and provides detailed annotations of functional sites, such as catalytic or binding interfaces. The database is regularly updated and can be searched by keyword or protein query sequence, with precalculated annotations updated several times daily. CDD is part of NCBI's Entrez system and is linked to other resources, facilitating comprehensive protein sequence analysis.