Raymond Aron, certainly one of the great political thinkers of the twentieth century, is known especially for his criticism of and committed struggle against totalitarianism. While even his contemporaries had become increasingly aware that his work in this connection was wide ranging and significant, it is clear today that he is a major figure among twentieth-century French intellectuals, and that his influence is especially pronounced among French liberals of the twenty-first century. We are therefore pleased to introduce, or to reintroduce, English readers to a lucid and demanding body of thought that makes no concessions to intellectual indolence or cowardice. Henry Kissinger loved to speak of Raymond Aron as his teacher, as someone who encouraged the effort to understand, explain, and interpret the movement of modern society by confronting reality and our awareness of it.