TM-align is a computer algorithm for protein structure alignment using dynamic programming and TM-score rotation matrix. An optimal alignment between two proteins, as well as the TM-score, will be reported for each comparison. The value of TM-score lies in (0,1]. In general, a comparison of TM-score smaller 0.2 indicates that there is no similarity between two structures; a TM-score greater 0.5 means the structures share the same fold. What is the difference between TM-score and TM-align? The TM-score program is to compare two models based on their given and known residue equivalency. It is usually NOT applied to compare two proteins of different sequences. The TM-align is a structural alignment program for comparing two proteins whose sequences can be different. The TM-align will first find the best equivalent residues of two proteins based on the structure similarity and then output a TM-score. The TM-score values in both programs have the same definition.