Berthold Gustav Gottlieb Delbrück (26 July 1842 in Putbus auf Rügen - 3 January 1922 in Jena) was a German linguist who devoted himself to the study of the comparative syntax of the Indo-European languages.
Delbrück studied at the universities of Halle and Berlin, and was appointed professor of Sanskrit and comparative linguistics at the University of Jena in 1869 where he remained until 1912. In 1871 he published a study of the subjunctive and optative moods in Sanskrit and Greek, which was the first thoroughly methodical and complete treatment of a problem in comparative syntax. His great achievement, however, was preparing volumes iii, iv, and v on syntax entitled Vergleichende Syntax der indogermanischen Sprachen in Grundriss der vergleichenden Grammatik der indogermanischen Sprachen (Outline of the Comparative Grammar of the Indo-Germanic Languages), published in Strassburg between 1893 and 1900 by Delbrück and Brugmann.
Besides the works mentioned, he wrote: