Reactive dyes are those whose ions or molecules contain groups which are reac- tive with other groups present in fibers to form covalent dye-fiber bonds. It has been known for many years that wool contains mercapto, amino and hydroxy groups, -SH, -NH2 and -OH, respectively, listed in decreasing order of reactivity, and that cellulosic fibers contain considerable num- bers of the latter. It takes two to tango. It is not enough to have a reactive dye mole- cule. One must also have a reactive group in the fiber. As early as 1885, Cross & Bevan made yellow and red esters of cellulose by a six-step synthesis. In these products, the dye was covalently bonded to the cellulose and the fastness to washing was excellent; but the reaction conditions were too severe and lengthy to be practical and the fibers were badly degraded (2,3). So, in 1885, the principle was clearly established that chemical, covalent bond- ing between dye and cellulose could result in dyeings with outstanding wetfastness. But the belief was also reinforced that the hydroxy group of cellulose was of very low reactivity and that reactive dyeing might require to be driven by severe reaction conditions. (Notice the subjectivity of “very low” and “severe”: the meaning is in the mind.) Whether the reasons were conscious or unconscious, for the next 70 years the reaction to form covalent bonds between the more reactive thiols and amino groups in wool and reactive dye species received more attention than that between cellulose hydroxy groups and reactive dyes. The emphasis was placed on reactive dyes for wool despite the fact that improving the already good wetfastness of the dyeings which could be achieved on wool was not a technologically important objective at that time. Because the first commercial fiber reac- tive dyes appeared so much more recently than most other important dye application categories, it is worthwhile to point out how complete the scientific and technolog- ical documentation is. Not only that, but many of those who worked with reactive dyes since their commercial inception are alive and kicking today, including several of the authors whose work is cited in the