The Neogrammarians (German: Junggrammatiker, pronounced [ˈjʊŋɡʁaˌmatɪkɐ] ^ⓘ, lit. 'young grammarians') were a German school of linguists, originally at the University of Leipzig, in the late 19th century who proposed the Neogrammarian hypothesis of the regularity of sound change.

According to the Neogrammarian hypothesis, a diachronic sound change affects simultaneously all words in which its environment is met, without exception. Verner's law is a famous example of the Neogrammarian hypothesis, as it resolved an apparent exception to Grimm's law. The Neogrammarian hypothesis was the first hypothesis of sound change to attempt to follow the principle of falsifiability according to the scientific method.

Subsequent researchers have questioned this hypothesis from two perspectives. First, adherents of lexical diffusion (where a sound change affects only a few words at first and then gradually spreads to other words) believe that some words change others. Second, some believe that it is possible for sound changes to observe grammatical conditioning. Nonetheless, both of these challenges to exceptionlessness remain controversial, and many investigators continue to adhere to the Neogrammarian doctrine.

Other contributions of the Neogrammarians to general linguistics were:

Leading Neogrammarian linguists included:

Despite their strong influence in their time, the methods and goals of the Neogrammarians have been criticized for reducing the object of investigation to the idiolect; restricting themselves to the description of surface phenomena (sound level); overvaluation of historical languages and neglect of contemporary ones.^{[citation needed]}