AbstractWithin the past twenty years, while much of the research and development appeal in the halogenation of fats and fatty derivatives has been associated with the evolution of new and useful derivatives such as arthritis cures and artificial rubber plasticizers, the principal utility of the halogenated fats still continues to be in the production of other materials through halogenated fats as reactive intermediates. Consider, too, the utility of halogenated fats reflected by the fact that considerable quantities of iodochloro fats are discarded down the sinks of our analytical laboratories after the Wijs or other iodine value (I. V.) determinations. Aside from the valuable utility of halogenation as an analytical tool, what‐ever the use of halogenated fatty materials may be, i.e., for new and useful halogenated products per se, or for use as intermediates for the productions of other materials, halogenation is capturing an ever‐increasing share of the effort being directed to the modification of the chemical and physical nature of fats. While the standard and well‐known methods of utilizing fatty acid chlorides as reactive intermediates continue to fluorish, the newer aspects of fat halogenation, as demonstrated by the development of fluorinated derivatives, and in the utilization of chlorination followed by dehydrochlorination for the production of more highly‐unsaturated fat molecules, illustrate a few directions in which progress is being made.