Data collection and analysis is nothing new in computer-assisted language learning, but with the phenomenon of massive sets of human language collected into corpora, and especially integrated into systems driven by artificial intelligence, new opportunities have arisen for language teaching and learning. We are now seeing powerful artificial neural networks with impressive language capabilities. In education, data provides means to track learner performance and improve learning, especially through the application of data mining to expose hidden patterns of learner behavior. Massive data collection also raises issues of transparency and fairness. Human monitoring is essential in applying data analysis equitably. Big data may have as powerful an impact in language learning as it is having in society generally; it is an important resource to have available, but one to use with care and caution.