Johann Karl Ludwig Gieseler, KH (3 March 1792 – 8 July 1854) was a Protestant German church historian.
In his tenth year he entered the orphanage at Halle, from which he duly passed to the university, his studies being interrupted in October 1813 by a period of military service, during which he was enrolled as a volunteer in a regiment of chasseurs.
In 1819 Gieseler was appointed a professor ordinarius in theology in the newly founded University of Bonn, where, besides lecturing on church history, he made important contributions to the literature of that subject in Ernst Friedrich Karl Rosenmüller's Repertorium, KF Stäudlin and HG Tschirner's Archiv, and in various university "programs."
Less vivid and picturesque in style than Karl Hase, lacking August Neander's deep and sympathetic insight into the more spiritual forces by which church life is pervaded, he excels these and all other contemporaries in the fulness and accuracy of his information.
His Lehrbuch der Kirchengeschichte, with its copious references to original authorities, is of great value to the student: "Gieseler wished that each age should speak for itself, since only by this means can the peculiarity of its ideas be fully appreciated."