In this paper we compare the code-switching (CS) patterns in three bilingual corpora collected in Wales, Miami and Patagonia, Argentina. Using the Matrix Language Framework to do a clause-based analysis of a sample of data, we consider the impact of structural relationships and extra-linguistic factors on CS patterns. We find that the Matrix Language (ML) is uniform where the language pairs have contrasting word orders, as in Welsh-English (VSO-SVO) and WelshSpanish (VSO-SVO) but diverse where the word order is similar as in Spanish-English (SVO-SVO). We find that the diversity of the ML in Miami is related to the diversity of degrees of proficiency, ethnic identities, and social networks amongst members of that community, while the uniformity of the ML in Wales is related to the uniformity of these factors. This is not so clear in Patagonia, however, where there is little CS produced in conversation. We suggest that the members of the speech community use Spanish or Welsh mostly in a monolingual mode, depending on the interlocutor and the social situation.