In the four years since Sullivan first pointed out the importance of the method of localization In homotopy theory, there has been considerable work done on further developments and refinements of the method and on the study of new areas of application. The Battelle Seattle Research Center therefore decided to act as host to a symposium on localization theory, which took place at the Center during the week of March 11 - 15, 1974. The opportunity was a particularly good one, since at that time, Guido Mislin and Joseph Roltberg were at the Center as Visiting Fellows.