In this chapter, it is argued that the study of World Englishes (WE) should assume a more central place in the analysis of variation and change in the context of language contact. Because they emerge from situations of bilingualism and contact, WE varieties are highly informative with regard to the structural issues of code-switching and convergence (also termed structural borrowing, transfer, interference, imposition). The inherently mixed nature of WE is shown here to mirror the diverse structural patterns that are commonly encountered in bilingual speech. It is argued that different mixing patterns arise in response to the social and medial embedding of WE vernaculars at the community, the individual, and the interactional levels. Social evaluations of relative prestige, individual projections of style, stance, and identity, and the complex nature of multilingual interaction conspire to bring about complex, new language structures.