Most paleontological textbooks deal with tracheates and chelicerates in only a cursory way because of their putatively poor fossil record. However, recent investigations into the paleobiology of these groups reveal that the fossil record is not only more extensive than previously assumed, but provides a wealth of information regarding both broad and detailed patterns of evolution of the two most diverse subphyla on the planet. Tracheata, including insects, entognaths and the various myriapod groups, are the most diverse subphylum. Insects alone are the most diverse class of animals known, outnumbering the combined species level diversity of all other animals. The Chelicerata, composed of the eurypterids, xiphosurids, arachnids and pycnogonids, are the second most diverse subphylum, with the diversity of arachnids exceeding all classes except for the insects. Consequently, not only does the evolution of tracheates and chelicerates provide an interesting story in itself, but these groups also provide us with insight into more general aspects of the evolutionary process that are of interest to the general evolutionary biologist as well as to the arthropod specialist.