Bilingual studies that have paid attention to phonetics in CS have normally involved carefully controlled experimental designs where stimuli are created to elicit a monolingual or a bilingual mode and the resulting production and perception behavior of the bilinguals is taken as evidence for or against their ability to switch at the phonetic level or whether they might be influenced by factors such as the base language (see Bullock, this volume). This chapter suggests that bilinguals may constantly move between bilingual and monolingual modes during the course of the interaction depending on the needs of the situation. Microanalyses of interactions between bilinguals and their mothers showed that the base language does not always determine the phonetic patterns of the bilingual’s utterance. Bilinguals constantly negotiate meaning and identity with their interlocutors and the phonetic detail of their utterances can reveal a lot about their convergence and divergence strategies.