For a number of reasons, the size of the Arabic textual tradition still remains a mystery to historians. The proliferation of digital libraries of premodern Arabic texts and the development of methods of textual analysis offer, however, a new means and opportunity to obtain our first data-driven view of this tradition. The paper will begin with an evaluation of the Arabic textual tradition through the analysis of the Hadiyyat al-`arifin, a bibliographical collection from the early 20th century. Building on the famous Kashf al-zunun of Hajji Khalifa (d. 1656), it offers sufficient information on about 8,800 authors and 40,000 titles to analyze a variety of dimensions of book production in the Islamic world. While showing that the rate of overall book production across the Islamic world steadily increased over time, the data also shows that regionally book production peaks during the reign of major Islamic dynasties that flourished in different periods across the Islamic world. The second part of the paper will focus on an overview of the textual interconnectedness of premodern Arabic texts that are now available in a number of digital collections (al-Jami' al-Kabir, Shamela, ShiaOnlineLibrary). A comparison of their contents with the bibliographical data from the Hadiyyat al-`arifin shows that these digitized texts---despite their impressive volume of about 7,800 unique texts (1.2 billion words) unevenly distributed across 14 centuries of Islamic history---are just a fraction of the entire tradition. Our computational analysis further shows that nearly all these texts are interconnected with each other through an extremely high volume of shared quotations, strongly suggesting that these digitized texts---despite representing a number of forms and genres---in fact form a clear sub-tradition. The final section of the paper will turn to one of the major nodes in this sub-tradition---"The History of Islam", a 50-volume biographical collection written by the Damascene scholar al-Dhahabi in the 14th century. After characterizing al-Dhahabi's extensive network of sources, the paper will examine commonalities among passages that are being quoted by al-Dhahabi and those that are being omitted by him, thus attempting to identify what may constitute the core elements of that generate this interconnectedness and create a textual tradition.