Until the very early Middle Ages, Slavic vocalism developed uniformly. Later it began to diversify. Causes of diversification included territorial dispersion and occupation of areas where non-Slavic tribes lived or where Slavs neighboured non-Slavs. Some areas retained archaic features; others began to develop innovations. Hence, smaller intersecting areas often arose with particular features. In addition to the five mandatory vowel segments, Slavic languages have additional regional segments. We distinguish at least the following: an area with phonological long vowels; the western periphery with diphthongs and additional intermediate segments between /i/ and /e/ and between /u/ and /o/; an area with additional central vowels; one with distinctive tonal features; one with reduction of unstressed vowels; areas with traces of nasal vowels; an area with a glottal stop; one with high frequency of vowel clusters (while the frequency ratio of vowels to consonants in text does not vary much).

This chapter provides an overview of phonologically conditioned synchronic alternations representative of Slavic languages. The vocalic processes covered are vowel reduction and resulting phonological neutralization patterns in unstressed syllables, vowel-zero alternations, alternations in vowel quantity due to compensatory lengthening or to rhythmic requirements, and alternations in vowel quality, such as fronting/backing and raising/lowering. The consonantal processes discussed include alternations in voicing, such as voicing assimilation and word-final devoicing, and palatalization before front vowels and as a result of assimilation in a consonant cluster. Some language-specific alternations are also discussed.

The detailed phonology of the word level, defined as the last lexical stratum. This is stratum 2 in English, which, like stratum 1 is word bounded, is structure preserving, and has access to word-internal structure assigned at the same stratum, but unlike stratum 1 is not cyclic and is not subject to the Strict Cycle Condition, allowing rules like Vowel Shift and Velar Softening to apply freely in nonderived contexts. Vowek Shift is a chain shift that affects stressed tense vowels by shifting high vowels to low and raising low vowels to mid and mid vowels to high, without creating any mergers. Some additional rules are required to ensure the final vowel qualities. Some tensing rules apply on stratum 1 or this stratum before Vowel Shift, another applies after Vowel Shift. Vowel reduction produces two or three vowels (depending on dialect), not just schwa as in SPE. Rules for consonants include Velar Softening, Palatalization, Spirantization, with interesting and complex ordering relations. Summary of the stratum 2 rules and their ordering.

The present contribution examines phonological processes attested in modern Germanic languages. Focus is placed on segmental changes belonging to one of the following types: assimilation, dissimilation, epenthesis, deletion, coalescence, vowel reduction, strengthening, and weakening. Although some reference is made to diachronic developments, the emphasis in the present article is on those processes that are active in the synchronic grammar.