Modifications mothers make when talking to young English-speaking children between the ages of 1;8 and 3;0 (average age=2;4) about words perceived to be familiar versus unfamiliar were investigated. Nineteen mothers and their children participated in two toy play tasks; one designed to elicit talk about familiar and unfamiliar animals and the other designed to elicit talk about familiar and unfamiliar actions. It was found that mothersʼ talk involving unfamiliar words differed from talk involving familiar words in a number of ways. Some modifications served to highlight the unfamiliar word which could assist in segmenting the unfamiliar word and mapping it to its referent. Compared to familiar nouns and verbs, unfamiliar nouns and verbs were produced more frequently in highly salient utterance positions and were paired more consistently with a clear nonverbal referent. Familiar nouns but, not verbs, were produced in longer utterances than unfamiliar nouns which could support the childʼs elaboration of the lexical representation of the familiar word.