The astrolabe was for many centuries the most popular of all astronomical instruments. Invented during the Hellenistic period, it proliferated in medieval times, especially in the lands of Islam and consequently also in Europe. The melon-shaped astrolabe is a special form of astrolabe. Unlike the commonly known planispheric instrument, it does not depend on stereographic projection. A description of its principles is to be found in the introduction and in the texts edited here. Making the instrument required elaborate mathematical procedures, which are themselves of considerable historical interest. Presented here are extended texts by Habash al-Hasib (9th century) and al-Biruni (d. 1048), together with extracts and references by other authors. The texts are accompanied by English translations and followed by detailed mathematical commentaries. "The results of Kennedy's and Lorch's research are impressive, and we should also mention the special philological competence of Prof. Paul Kunitzsch who was in charge of all the editions of Arabic texts which appear in the book. This book contains practically all the information available on this kind of instrument." Zeitschrift fuer Geschichte der arabisch-islamischen Wissenschaften "Kennedy, Kunitzsch and Lorch have provided a very careful and knowledgeable examination of the subject. This book deserves to be in the library of all those interested in astrolabes and instruments as well as Islamic astronomy and mathematics, whether they read Arabic or not." Nuncius .