Abstract The normal result of language contact is widely assumed to be convergence, as manifested in classic Sprachbünde and caused through metatypy, cognitive economy, shared norms of conversational practice, etc. Yet at the same time there is growing evidence that contact can also produce divergence, originating with Larsen’s idea of ‘neighbour opposition’) and developed through Thurston’s work on eseterogeny (elaboration of difference and impenetrability) to account for the apparently deliberate cultivation of language difference found in many parts of Melanesia. I argue that contact-induced divergence is more prevalent than previously thought, drawing on case studies from New Guinea and Northern Australia. Crucial ingredients are mechanisms for generating divergent structures (psycholinguistic, systemic), social settings favouring the linguistic signalling of group-membership distinctions, and social processes of linguistic ideology and praxis selecting for distinct structural options as social signalling devices.