Walker Percy differs from other American novelists in that he started writing fiction relatively late in life, after being trained as a physician and after considerable reading and writing in philosophy. Although critics have appreciated Percy's skills as a writer, they have seen Percy above all as a novelist of ideas, and, accordingly, the majority of critical articles and books about Percy has dealt with his themes, especially his philosophical themes, as well as with his philosophical sources. This study explores, therefore, the critical response to philosophical ideas in Percy's five novels to date, as evidenced first by reviews, then by the later articles and books. The critical response developed gradually as critics became aware of Percy's aims and pointed out his use of Christian existentialism and his attacks upon Cartesianism, Stoicism, and modern secular gnosticism. These critical evaluations of Percy's philosophical concerns have sometimes overshadowed interest in his more purely artistic concerns. However, the more a reader understands the underlying philosophical concepts that inform Percy's novels, the more he may understand what Percy is trying to say and the more he may appreciate Percy's accomplishment in expressing his philosophical ideas so skillfully in fictional form. Critics and readers may enjoy Percy's novels without knowing much about his philosophical ideas, but they cannot fully understand them. Thus this study concludes that the critical response to philosophical ideas in Percy's novels has done both Percy and Percy's readers a service.