Switching language is costly for bilingual speakers and listeners, suggesting that language control is effortful in both modalities. But are the mechanisms underlying language control similar across modalities? In this study, we attempted to answer this question by testing whether bilingual speakers incur a cost when switching to a different language than the one just used by their interlocutor. Pairs of unbalanced Dutch (L1) -English (L2) bilinguals took turns naming pictures in a pure Dutch, a pure English, and a mixed-language block. In the mixed block, one participant (Switching Participant) voluntarily switched between Dutch and English, whereas the other (NonSwitching Participant) named all pictures in Dutch. Within the mixed block, the Non-Switching participant took longer to name pictures when the Switching participant's response on the preceding trial had been in English rather than Dutch, and this local switch cost was larger the more the NonSwitching participant was proficient in English. Additionally, there was strong cross-person itemlevel interference: The Non-Switching participant named pictures more slowly in Dutch if the Switching participant had previously named those same pictures in English rather than Dutch.These findings indicate that comprehension of utterances produced by another speaker in L2 makes subsequent production of L1 utterances more costly. We interpret this as evidence that language control mechanisms are shared between comprehension and production, and specifically that bottom-up factors have a considerable influence on language selection processes in both modalities.Keywords: voluntary language switching; joint task; comprehension; production. Bilinguals often switch between their languages, especially during informal conversations with other bilinguals (e.g., Grosjean, 2001). However, switching language leads to slower responses in laboratory tasks, both when bilinguals produce a switch (e.g., Meuter & Allport, 1999) and when they comprehend a switch (e.g., Thomas & Allport, 2000). Showing that language switches are costly to process in comprehension and to execute in production is relevant for theories of bilingual dialogue since bilingual interlocutors tend to switch between their shared languages within their respective turns (e.g., Grosjean, 2001). But furthermore, in some bilingual conversations, each interlocutor consistently uses only one language (normally her first language, L1), so that switches occur between turns (if the two bilinguals have different L1's). Thus, bilinguals may also be confronted with switches from comprehension (of their interlocutor's utterance) to production (of their own utterance).The goal of the present study was to investigate whether comprehension of utterances produced by another speaker in one's second language (L2) makes subsequent production of L1 utterances more costly. As we explain below, the occurrence of cross-person switch costs is compatible with theories of bilingual lexical selection that assume shared language contro...