This encyclopedia has been formed in three volumes and 30 chaptrrs based on different themes. The editors have compiled the work in such a way that the essays in each volume are related to one another in terms of theme. Wach essay is written by world class experts in each field. This distinguished work is undoubtedly one of the most important authoritative works ever written on the sciences of the Islamic era. In addition to the well- planned structure, among the special characteristics of this work one can mention its prose which follows standard prose for encyclopedias, abundance of references, scientific authority of the essays, as well as bibliography. The extensive and specialized bibliography on the history of sciences at the end of each volume based on the themes familiarize the reader with the latest and the source of each field.