This post on the Islamic Studies blog is an introduction to trustworthy editions of Arabic manuscripts. It is important to understand the difference between commercial and academic presses before starting primary source research, and the post names some commercial presses to avoid. The blog also has a wealth of information on primary sources for Islamic studies in Arabic, as well as lists of the most important sources for topics not covered here (hadith, Qur'an, fiqh, etc.).

A repository of digitized texts from libraries and other institutions worldwide. Note that to find all books by one author with an Arabic name, it might be necessary to search using different spellings.

Repository of digitized items from around the world hosted by the Library of Congress. The link above filters the materials in Arabic dated between 500 and 1900 CE, but these filters can easily be adjusted using the panels on top and on the left-hand side of the screen. Image quality is excellent, as is usability. The text search function does not work for Arabic script.

Archive.org is a growing collection of digitized texts. Searching can be difficult since Metadata for digitized objects varies substantially depending on the institution or person who uploaded the material. For Arabic materials, a simple search by author name or title in Latin characters is recommended.

An open digital library Arabic language content in the public domain drawn from collections at distinguished research libraries. Includes scholarly editions of classical works (histories, geographies, scientific texts, etc.). Search available in Arabic or English.

A collection of digitized manuscripts, published books, and maps in Islamic languages from Harvard University's libraries and museums. Materials range from the tenth century CE to today, and include works on history, geography, law, rhetoric, logic, philosophy, grammar, biographies, and scientific texts.

A repository of classical Arabic sources, searchable or navigable via a subject tree. The texts are transcribed onto the website itself, so information about the edition, notes, and references are absent, but the texts are fully searchable. It is recommended that this be used in conjunction with published scholarly editions in print or digitized form. The Website is in Arabic.

A digital public library of Arabic and Islamic culture, including searchable texts of historical works and encyclopedic entries on personalities, places, monuments, and even flora and fauna of the Middle East. Note: you must sign up for a user account (takes a day or two).

Website featuring access to the written heritage of the Islamic world. See especially the Manuscript Center under the Publications tab. Website available in English and Arabic.

AMIR (Access to Mideast and Islamic Resources) is a blog keeping track of open access resources related to the Middle East. Use the search bar on the top right to find authors or names of texts that have been digitized, or browse using the subject tag list on the right below the search bar.

Project coordinated by the Bibliotheca Alexandrina to make classics of Islamic thought from the modern period available in Arabic and translation, mediating the focus of scholarship on the earlier periods.

Website featuring digitized and fully searchable texts of five of the most important classical Arabic-language dictionaries: Lisān al-‘arab (Ibn Manẓūr, d. 1312/711 AH); Maqāyis al-lugha (Ibn Fāris, d. 1004/395 AH); al-Saḥḥāḥ fī al-lugha (Jawharī, d. ca. 1009-1010/400 AH); al-Qāmūs al-Muḥīṭ (Fīrūzābādī, d. 1415/817 AH); al-‘Abāb al-zākhir (Saghānī, d. ca. 1252/650 AH). Type an Arabic word in the search bar at the top of the screen to return every instance of its usage in these five dictionaries.

Digitized version of Edward William Lane, Arabic English Lexicon (London: Williams and Norgate, 1863). Lane's dictionary is considered a good source for classical and archaic Arabic usage. The digitized book is not fully searchable, but one can navigate through letters and page headings (the first word root on the page).

Online Arabic-English dictionary for modern usage. Users can search for roots, words, or English translations in Fusha (MSA) as well as Moroccan, Levantine, and Egyptian dialects. This is a one of a kind resource.

The authoritative English-language source for information on people, places, and events in the history of Islam. Note that this publication uses a unique transliteration system. For Arabic letter qaf use "k" and for Arabic letter jim use "dj" (e.g. "Kur'an" and "Djazira" instead of "Qur'an" and "Jazira"). Access: full access to Encyclopaedia of Islam is limited to subscribers or subscribing institutions. You may freely search the database without a login but only partial articles are visible. MIT students can login with their Kerberos account via Vera here.

Encyclopedia dedicated to Iranian civilization in the Middle East throughout the ages. Excellent source of information for places and people in greater Iran. Online content is accessible to all.

Turkish version of Encyclopedia of Islam, including many significant additions, especially of Ottoman and Turkish subjects. Open access and fully searchable text in Turkish.

This list of books, Websites, and other digital tools developed by Dagmar A. Riedl contains a wealth of information on manuscript studies. Especially helpful are the resources listed under the headings "Digital Databases of Manuscripts in Arabic Script," and "Resource Websites."

A regularly updated list of collections of Islamic manuscripts with open access material, maintained by AMIR (Access to Middle East and Islamic Resources).