Examination of the early literature attests to the fact that the study of copolymerization was initiated when polymer science was in its infancy. It has continued to grow to a subject of major importance and has been a source of interest to both academic and industrialist alike. The wide spectrum of structures and properties available in the statistical copolymer has made this a fruitful field of exploration, but one particular and more restricted form which has held its own fascination for many is the limiting case of the strictly alternating copolymer. This is formed, in the ideal situation, when two monomers in a reaction mixture add consecutively to create a polymer chain with a regular {ABABAB} structure, irrespective of the monomer feed ratio. When this happens the resulting copolymer will always have the same composition, a feature which can be advantageous but also somewhat restrictive, as the ability to vary the properties is then limited. Within a series entitled Speciality Polymers it seems appropriate then to deal with this subject, particularly as no previous attempt has been made to draw together the various facets of alternating copolymerization into one volume. It also seems timely to present a more unified picture of the subject which will also illustrate the progress made.