None of his subsequent works have the same unmistakable Grothendieck flavor of this first book. Both Grothendieck and Quillen sought for what was absolutely fundamental in a problem, but where Grothendieck found the essence in generality, Quillen’s guiding conviction was that to understand a mathematical phenomenon one must seek out its very simplest concrete manifestation. He felt he was not good with words, but his mathematical writings, produced by long agonized struggles to devise an account that others would understand, are models of lucid, accurate, concise prose, which, as Michael Atiyah has pointed out, are more reminiscent of Serre than of Grothendieck.