Repeat amino acid sequences are important in protein structure, disorder, function and evolution. Repeats of some amino acids exist in proteomes across species.This volume highlights:Which repeat sequences have pathogenic consequences and why?Repeats which lead to surface hydrophobic clusters and their importanceRole of aromatic amino acid clusters in protein‐protein and protein‐drug interactionsCell‐penetrating peptides and Elastin‐like peptidesUnusual phenomenon of fluorescence observed with repeats of some non‐aromatic amino acidsThe use of residue cluster classes to represent protein structure and model structure‐function relationships.