The DSSP algorithm is the standard method for assigning secondary structure to the amino acids of a protein, given the atomic-resolution coordinates of the protein. The abbreviation DSSP stands for Define Secondary Structure of Proteins.

DSSP recognizes eight types of secondary structure (each identified by its own symbol), depending on the pattern of hydrogen bonds. The 310 helix, alpha helix and pi helix are symbolized as G, H and I, respectively and the algorithm can also recognise beta bridges (B), and beta sheets (E). Sheets with beta_bulges are also symbolised by E. The remaining types are T for turn (featuring a hydrogen bond typical of a helix), and S for a region of high curvature (if the angle between the vector from Cαi to Cαi+2 and the vector from Cαi-2 to Cαi is less than 70°.