A distinguished scholar surveys centuries of conflict between Christianity and Islam. Vivid, concrete examples epitomize the characteristics of successive eras. Crusades, conversion, coexistence were the choices; the need for knowledge of Moslem beliefs, R. W. Southern says, competed with “fear of contamination.” Medieval Christians faced “all the problems with which, in a different context, we are familiar.” His book distinguishes three phases: first, four centuries of indifference or distortion; second, a 13th-century attempt to evaluate Islam; finally, the 1450s—when various thinkers achieved unique insight into central issues.