The OB-fold is found in all three kingdoms and is well represented in both sequence and structural databases. The OB-fold is a five-stranded closed β barrel and the majority of OB-fold proteins use the same face for ligand binding or as an active site. Different OB-fold proteins use this ‘fold-related binding face’ to, variously, bind oligosaccharides, oligonucleotides, proteins, metal ions and catalytic substrates. Recently, a number of new structures with OB-folds have been reported that augment the variation seen for this set of proteins whilst conserving the characteristic fold and binding face. The conservation of fold and a functional binding face amongst many structures provides a model for investigating the evolutionary trajectory of sequence, structure and function.