Chemical protein synthesis is a field in transition. Previously, the synthetic accomplishment itself was the major focus of work in this field. Increasingly, chemical synthesis is now being applied to understanding how biological function originates in the structure of the protein molecule. A novel approach--'chemical ligation', which is the chemoselective reaction of unprotected peptide segments in water at pH7--has made the total synthesis of proteins a robust and practical route to the study of structure-function relationships. For certain protein families, chemical protein synthesis is the most effective way to obtain functional proteins direct from genome sequence data.