A major difference between the refolding of proteins in vitro and the in vivo folding process, in which we include localization and assembly, is the need for additional factors in vivo, apart from the protein product itself. Thus, the amino acid sequence of a naturally selected protein contains not only the information specifying its three-dimensional structure, but also the information that enables these factors to recognize the nascent polypeptide. In this review, we consider how this latter information may be encoded and, in turn, interpreted by binding species.