Studies into the use of Twitter for language learning have mostly been small-scale evaluations undertaken by teachers researching the effectiveness of their own initiatives to use it with their students. To date, there has not been a large quantitative study of how language learners use Twitter autonomously. This paper reports on a large-scale study (n=370) of language learners who use Twitter. It provides a participant profile, their practices, and beliefs about how helpful Twitter is as a tool for language learning. The results provide the first profile of the autonomous user of Twitter as a language learning tool, show very positive attitudes towards the use of Twitter, and provide evidence that learners learn new vocabulary and culturally-relevant information about the areas where the target language is spoken. Many learners engage in production of target language output and make the most of the opportunities Twitter presents to be exposed to target language input and interaction with native speakers, making Twitter a useful tool for their autonomous language learning development.