The Structural Classification of Proteins (SCOP) database provides a comprehensive and detailed description of protein structures, focusing on both evolutionary relationships and structural similarities. The classification is hierarchical, with levels including family, superfamily, fold, and class. Family and superfamily levels describe evolutionary relationships, while the fold level describes geometric relationships. SCOP includes links to atomic coordinates, structural images, interactive viewers, sequence data, conformational change data, and literature references. The database is freely accessible via the World Wide Web at http://scop.mrc-lmb.cam.ac.uk/scop/. It is organized as a tree structure, allowing users to browse through different levels of classification or search by sequence similarity, keywords, or PDB identifiers. The SCOP database serves as a powerful tool for researchers and students, providing easy access to data and images, and facilitating comparisons of protein structures.The Structural Classification of Proteins (SCOP) database provides a comprehensive and detailed description of protein structures, focusing on both evolutionary relationships and structural similarities. The classification is hierarchical, with levels including family, superfamily, fold, and class. Family and superfamily levels describe evolutionary relationships, while the fold level describes geometric relationships. SCOP includes links to atomic coordinates, structural images, interactive viewers, sequence data, conformational change data, and literature references. The database is freely accessible via the World Wide Web at http://scop.mrc-lmb.cam.ac.uk/scop/. It is organized as a tree structure, allowing users to browse through different levels of classification or search by sequence similarity, keywords, or PDB identifiers. The SCOP database serves as a powerful tool for researchers and students, providing easy access to data and images, and facilitating comparisons of protein structures.