Adjectives and adverbs are two parts of speech whose prototypical function is to qualify or modify the mean- ing of basic grammatical categories such as nouns and verbs. Adjectives and adverbs share important char- acteristics. Some words can be used as both adjectives and adverbs, and some grammatical structures using adjectives or adverbs are very similar. Because there are many ways to qualify something, many grammatical constructions use adjectives and adverbs. In some cases, the nouns or verbs qualified are omitted or implied, meaning that adjectives and adverbs are sometimes used independently from nouns or verbs and have a predicate or deictic value. This entry reviews the functions of adjectives and adverbs and then discusses the two categories in relations to language acquisition and language disorders.