Hermann Friedrich Lossen (November 7, 1842 – August 27, 1909) was a German surgeon born in Emmershäuser Hütte, Hesse.
He studied under Carl von Voit (Munich), Friedrich Daniel von Recklinghausen (Würzburg), Bernhard von Langenbeck (Berlin) and Theodor Billroth (Vienna), earning his medical doctorate in 1866 from the University of Würzburg. In addition he served as an assistant to Richard von Volkmann at the University of Halle and to Gustav Simon at the University of Heidelberg. In 1866 he became habilitated for surgery at Heidelberg, where in 1874 he was appointed associate professor.
Lossen was author of a revision of Carl Hueter's Grundriss der Chirurgie (Outline of Surgery), which was published over several editions. Other noted works by Lossen include: