Karl Franz Otto Dziatzko (27 January 1842 – 13 January 1903, Göttingen) was a German librarian and scholar, born in Neustadt, Silesia.
From 1859 to 1863 he studied classical philology at the universities of Breslau and Bonn. At Bonn, he was influenced by philologist Friedrich Wilhelm Ritschl and worked as an assistant at the university library. In 1863 he received his doctorate with a thesis on the prologues of Plautus and Terence. Following graduation, he worked as a schoolteacher in Opole and then in Lucerne (from 1865).
In 1871 he became head librarian at the University of Freiburg, where he also obtained his habilitation the same year. After a brief stint as a schoolteacher in Karlsruhe, he was appointed director of the university library at Breslau (1872). Here, he headed a comprehensive reorganization of the library that included rules for a new alphabetical card catalog that became a model for the Preußische Instruktionen. From 1886 until his death, he was director of the university library and professor of library science at the University of Göttingen.
With educator Friedrich Althoff, he strove for reforms pertaining to academic librarianship during the latter part of the 19th century. At Göttingen, he was instrumental in the creation of a professional librarian association (initially a section within the Philologenverbande (Philology Association). Also, he made significant contributions in the fields of "Gutenberg research" and incunabula studies, that included a complete incunabula catalog
Among his publications are a text edition of the comedies of Terence (1884); "Instruktion für die Ordnung der Titel im alphabetischen Zettelkatalog der königlichen und Universitätsbibliothek zu Breslau" (1886); and "Untersuchungen über ausgewählte Kapitel des antiken Buchwesens" (1900). The publication of 1886 is said to be the basis of K. A. Linderfelt's "Eclectic Card Catalog Rules" (Boston, 1890).