This chapter summarizes sound variations specific to the contact between class prefixes and the noun and adjective stems. It also addresses special class agreement and the issue of invariable adjectives and pronouns. It shows main phonetic features of Swahili vowels. It also shows how verb-derived nouns and those that naturally begin with a vowel tend to apply special rules, such as vowel sequences between the prefix and the stem, as opposed to the pronouns, adjectives, and original noun stems, which tend to trigger vowel merger or consonant change. Class prefixes composed of single vowel generally become semi-vowels when they are connected to a non-identical stem vowel. For prefixes composed of a consonant and a vowel, the prefix vowel is generally retained before an identical stem vowel within nouns and infinitive forms. Most adjectives and pronouns vary in accordance with the nouns they are related to in a given sentence; some of them do not vary.