This study discusses the two most outstanding features of Flann O'Brien's work: his comic approach, and his thematic and narrative complexity. The first two chapters explore O'Brien's use of comedy throughout his development as a writer, and examine the nature of his humour in its Irish context. Subsequent chapters deal with the four major comic novels individually, studying the author's treatment of his major theme of man's failure to establish himself in a reasonable relationship with reality, and in particular the tonal and linguistic complexity of the narrative used to pursue this theme.