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In the study of historical linguistics and phonetic change, a 'chain shift' is a type of sound shift in which a group of sounds all change at about the same time, with some sounds taking the place of others. Chain shifts may be confined to certain isoglosses; they may also spread over the years.
Examples of historical chain shifts in English are the Great Vowel Shift in the 15th century, and the ongoing Northern cities vowel shift.
While a chain shift usually occurs as a set of vowel shifts, chain shifts can also occur in consonants. For example, a set of plosives that have a voiced/voiceless distinction may shift to have an aspirated/unaspirated distinction. In this case, the voiceless consonants become aspirated, and the voiced consonants become voiceless.
A famous example of such a shift is the well-known Grimm's Law, which turned the Proto-Indo-European voiceless/voiced/breathy-voiced distinction into a fricative/voiceless/voiced distinction in Germanic. Another is the High German consonant shift which separates Germanic from Modern German.