This study applies the non-linear models of Autosegmental and Metric Phonology to the description of phonological change processes. The following diachronic phenomena are discussed: (1) Verner's Law, (2) vowel lengthening in Middle English, (3) vowel lengthenings and shortenings from Middle High German to New High German. These historical changes are seen to be subject to universal prosodic restrictions retaining their validity for present-day language systems.