Numerous examples of the three-dimensional structures of peptides complexed with their biological partners have been determined recently by both X-ray crystallographic as well as modern NMR techniques. These provide a basis for the evaluation of concepts proposed earlier regarding peptide recognition, and determine the range of recognition motifs which are commonly used in biological systems. Two extremes of motifs have emerged: one linear, with the peptide backbone providing many of the recognition elements; the other dominated by interactions with the side chains, often held in β-turns. Recognition is concentrated in a few key anchor residues arranged in a particular three-dimensional arrangement, which sometimes but not always requires a particular backbone conformation. The influence of the receptor on the peptide conformation is clearly evident, and argues against trusting conclusions based solely on experimental data from the peptide alone.