This volume contains a selection of papers presented at the Fifth Conference on the Foundations of Arab Linguistics (FAL V, Cambridge, 2018). The first part of the book deals with Sībawayhi’s Kitāb, the oldest known treatise of Arabic grammar: after providing insights on some of its specific terminology, these chapters evaluate its place as a source within the long-term tradition of grammatical studies. The second part of the book focuses on parallel developments in the Arabic grammatical theory, both in the classical and postclassical periods up to the 15th century. Some contributions also address the relationship between grammar and other disciplines, notably philosophy and Qurʾānic exegesis. As such, this volume aims to deepen our knowledge of the development of linguistic theories in the Islamicate world.