Since the nineteenth century, the modernisation of Arabic vocabulary has been subject of a great concern for Arab scholars who are loyal to the language while aware of the need to adapt it to the demands of the modern world. This thesis attempts to present a comprehensive view of the subject by examining linguistic and extra-linguistic aspects of the process of lexical development in Modern Standard Arabic. The thesis comprises six chapters: Chapter One: is a brief introduction to the emergence of the movement for cultural and linguistic revival in the Arab world, leaders of linguistic reform, and the Arabic language academies. Chapter Two: examines the phenomenon of Ishtiqāq (Derivation) in Arabic, and its role in providing the language with native means of generating new lexical items. Chapter Three: discusses the assimilation of foreign words. It investigates the concept of borrowing in both classical and modern theory, and presents a description and analysis of this process as adopted for Modern Standard Arabic. Chapter Four: deals with the methods of Tarkīb and Naẖt (Compounding and Blending), and assesses their significance in the growth of Arabic vocabulary. Chapter Five: gives a brief introduction to the question of terminology formation and reviews the terminological activities in the Arab world which, aim at the standardization of current terminological work and the creation of a unified Arabic vocabulary. Chapter Six: provides a brief summary of the conclusions and findings of this study.