Karl Friedrich Eusebius Trahndorff (18 October 1782 – 1863) was a German philosopher and theologian.
He was born in Berlin. The son of a musician, from the age of twelve Trahndorff attended the school in Oels (now Oleśnica), where his father had been appointed chapel director by the Prinz von Brunswick-Lüneburg, Frederick August I. From 1801 he studied theology and philology in Königsberg, and on completion of his studies he began a career as a high-school teacher, mostly at the Friedrich-Wilhelm Gymnasium in Berlin but with several years in Białystok.
As a religious and philosophical writer, Trahndorff belonged to the supernaturalist camp, opposed to theological rationalism and emphasizing the indeducible, supernatural and mystical nature of religious revelation, by implication minimizing the ability of human reason to grasp the content of faith. His polemical work Theos, nicht Kosmos! attempted to combat the growing popularity of Alexander von Humboldt's Kosmos, which he considered incompatible with scripture.
Trahndorff's Ästhetik oder Lehre von Weltanschauung und Kunst is relevant to students of German Romanticism; it used the word Gesamtkunstwerk for what is believed to be the first time.