Kâtip Çelebi, or Haji Khalifa, is celebrated in the countries of the Islamic East as the author of the Kaşf az-Zunūn (The Removal of Doubt from the Names of Books and the Arts). This bibliographic encyclopedia of books and sciences was based on the Miftāḥ al-Saʿāda wa-miṣbāḥ al-Siyādah by the c.16th Ottoman historian, Taşköprüzade. However the Kaşf substantially enlarges it, cataloging titles of about 15,000 book, about 9,500 names of authors, and about 300 sciences and arts. At the age of twenty-five in 1633 while in Aleppo he began compiling and composing the work that occupied him for the next twenty years, until its completion in 1652. An account of this is contained in his book "", where he writes: "On my stay in Aleppo, I would visit bookshops to browse, and then when I had returned