This critical edition of al-Isfizāri’s book deals with the field of mechanics, known by early Muslims as “the sciences of weights and mechanical devices” (‘Ilmay al-Athqāl wal-Ḥiyal). The book introduces the theory of the “steelyard” and its applications. It extensively describes and provides exhaustive details on a large group of mechanical devices. Its contents are organised into seven parts. Reading this work of Isfizāri enhances the knowledge of historians and researchers of Islamic heritage and specifically the history of Arab mechanics. It also confirms both the originality and innovative characteristics of the Arab contribution to the field of machinery in terms of using mathematics and physics in both experimentation and theory. The work demonstrates how Muslim scientists’ ventures had substantially participated in transferring and developing scientific knowledge in addition to elaborating its value from the history of technology and a mechanical engineering perspective.