'Mixed Language,' a characteristic pattern of language use among African township residents in South Africa, may well include words or full constituents from several languages. However, from both a structural and a social perspective, such speech has a systematic nature. In reference to grammatical structure, within any CP (projection of COMP) showing codeswitching, only one language (the Matrix Language) provides the grammatical frame in the data studied. Also, while speakers from different educational levels engage in codeswitching with similar frequencies, the types of codeswitched constitutents they prefer are different. In reference to the social use of language, we argue that specific patterns of codeswitching indicate how language is both an index of identity and a tool of communication in South Africa. In the codeswitching patterns they use, speakers exhibit strong loyalty to their own first languages. Yet, because they recognize that codeswitching facilitates communication with members of other ethnic groups, they use a number of codeswitching strategies as a means of accommodating to their addressees and simultaneously as a means of projecting multiple identities for themselves.