Abstract Between the 8th and the 14th centuries, a paradigm of grammatical research of remarkable sophistication, scope, and depth arose in the Arab world. This chapter is devoted to a presentation of some of the results of the Arab grammarians in the areas of morphology and phonology. Emphasis is laid on the architecture of their model of grammatical description and on their mode of argumentation. A body of evidence from the verbal system of Classical Arabic is presented along with some of the questions a contemporary reader would raise. The approach and answers provided at various times by Arab grammarians are laid out and critically discussed. Numerous parallels with contemporary linguistic theory are drawn.