Twitter can be used as a language learning tool and this potential has been identified by a number of scholars. This chapter presents an overview of the identified potential of Twitter as a language learning tool and presents an overview of different studies carried out to provide evidence of language learning using Twitter in different contexts. It concludes that, although there is evidence of language acquisition in formal contexts, more research is needed to inform how Twitter is used in informal settings. [For the complete volume, "Innovative Language Teaching and Learning at University: Integrating Informal Learning into Formal Language Education," see ED585162.]