The MDAH/ORINS group was not the only one working on a cobalt-60 therapy unit, and the other groups are briefly described in this chapter; there were two in Canada and one in Los Angeles. Because of this, priority claims concerning the development of the cobalt-60 unit have always existed. This is looked at briefly, and a chronology of the development of such units is presented. The subsequent commercial development and world-wide success of cobalt-60 radiotherapy is looked at with the recognition that Fletcher played a major role in the development of the clinical use of cobalt-60 units. Although the use of cobalt-60 units peaked in the 1990s and was replaced by linear accelerators, they are still extensively used, especially in developing countries. However, this has not been without cost since there is potential for serious misuse. Two such examples are given, one concerning the incorrect application of the decay of the radioactive cobalt-60, which resulted in serious over dose to hundreds of patients, the other concerning the incorrect disposal of the radioactive source. Of great importance is the use of cobalt-60 as the standard radiation in national calibrating laboratories.