From a reexamination of the X‐ray studies of the crystal structures of 27 N‐acyl‐amino acids, peptides and their derivatives and 30 linear peptides, it is concluded that specific formation of short intermolecular hydrogen bonds (2.5 to 2.6 å) from the carboxyl OH to the N‐acyl oxygen is an important feature for N‐acyl‐amino acids. For N‐acyl‐N1‐amides, the formation of hydrogen bonds 2.7 to 2.9 å long between N(acyl)‐H … O(amide) is strongly preferred. The dihedral angle δ between the N‐acyl and carboxyl groups or adjacent amide groups shows a preference for values near 20° or 90° for N‐acylamino acid