Die drei Fragezeichen (Hörspiele) is a 137-book series with 137 released primary works first released in 1964 with contributions by Robert Arthur, Alfred Hitchcock, Jens Wawrczeck, William Arden, M.V. Carey, Nick West, Marc Brandel, Megan Stine, Henry William Stine, G.H. Stone, Peter Lerangis, Brigitte Johanna Henkel-Waidhofer, André Marx, Ben Nevis, André Minninger, Katharina Fischer, Marco Sonnleitner, Ingeborg Urspruch, Astrid Vollenbruch, Kari Erlhoff, Hendrik Buchna, and Christoph Dittert.