Publisher Summary This chapter describes the chemical approaches of protein engineering that are amenable to the generation of mutants of hemoglobin (Hb). The need and significance of the chemical approaches of protein engineering in this era of oligonucleotide-directed site-specific mutagenesis are also emphasized. The discussions are limited to aspects relevant to Hb chemistry and the general principles of several approaches are discussed. The recombinant methods of protein engineering, although efficient and most of the time quite simple, are limited in their ability to choose from a repertoire of 20 natural amino acids. The need for a higher flexibility, particularly for the introduction of the noncoded amino acids at a given site, is apparent in the recent attempts to develop in vitro translation systems. The chemical synthetic approach to systematic variations of protein structure, in principle, is a much more general methodology than is site-directed mutagenesis. It offers a greater flexibility for the site-specific variation of the protein structure: incorporation of noncoded amino acids or introduction of amino acids with spectroscopic probes or photoactive functional groups.