The Antibody Enigma is a somewhat personal view of the antibody diversity question from two investigators who have spent the past 18 years trying to penetrate the enigma. It is not and was not meant to be an all-embracing comprehensively referenced review of the subject of antibody diversity. Because of the subjective viewpoint, there are un­ doubtedly omissions of data that others consider to be seminal, and if we have offended anyone by omitting their own contribution we sin­ cerelyapologize. We have lived with "The Enigma" on and off for the past two years. It has been both hard work and good fun but, above all, it has been a learning experience. There were several difficult decisions to make in putting together the final text, but perhaps the most difficult was de­ ciding upon a stopping point. The field of antibody diversity is presently enjoying an unparalleled expansion of information, and because of this it was very tempting to await further developments in hopes of tying up as many loose ends as possible. This was decided against for several reasons; the major factor was that the project was growing burdensome for both of us. From a more objective point of view this appears to be a reasonable time to stop our exposition.