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Tryptophan, an essential amino acid, exists in a number of conformations and adopts cationic, anionic, and zwitterionic forms at various pH values. On page 595, Uppula Purushotham and G. Narahari Sastry report a comprehensive computational analysis using DFT, dispersion-corrected DFT, and MP2 methods, quantifying the role played by various noncovalent interactions that impart stability to tryptophan dimers. They also analyze dimers of tryptophan residues in Protein Data Bank (PDB) structures. The cover depicts the various ionic forms of tryptophan and selected orientations of tryptophan dimers obtained from the PDB.