The Library Companion; or the Young Man's Guide, and the Old Man's Comfort, in the Choice of a Library

De Simone Company Booksellers specializes in early Italian books and manuscripts, mostly in the fields of social science, history, antiquarian bibliography and illustrated books. The owner, Daniel De Simone, has a particular interest in books, manuscripts, and ephemera printed in, or about, the history of Ferrara, Italy. The business also deals in 19th-century Americana and fine books in all fields and languages.

De Simone Company Booksellers enjoyed its second opening as a book company in 2018 after a seventeen-year hiatus. Originally established in 1978, De Simone Company bought, sold, and evaluated rare books, manuscripts, and prints for twenty-two years before closing, when De Simone accepted the position as Curator of the Lessing J. Rosenwald Collection at the Library of Congress.

De Simone held this position for fourteen years before moving to the Folger Shakespeare Library as the Eric Weinmann Librarian. In this position, he managed seven departments, including acquisitions, exhibitions, conservation, research services, and the Library's book, manuscript, and art collections. He held this position for three years before retiring in 2017 and reopening De Simone Company Booksellers.

Because of his experience in both the book trade and rare book librarianship, De Simone consults with institutions about the development and evaluation of their library collections. He is the author and editor of a number of books and articles on the history of book illustration and early bibliography.

He is a member of the ABAA (Antiquarian Booksellers' Association of America), the ILAB (International League of Antiquarian Booksellers), the Print Council of America, the Grolier Club, the Association Internationale de Bibliophilie, the American Printing History Association, the Bibliographical Society of America. He is also the Treasurer of the Antiquarian Book Seminar Foundation, a 501c3, which support the Colorado Antiquarian Books Seminar (CABS). Recently he has been appointed Secretary of Breslauer Prize for Bibliography by the International League of Antiquarian Booksellers.