An enduring contribution of Richards Sparks' work has been his exploration of the relationship between a learner's first language (L1) and a language that he or she learns subsequently (L2). The present paper considers that relationship from the perspective of learners and teachers of a 'foreign' language in classroom settings. The paper first sets the broader context by looking briefly at the recently developed concept of 'translanguaging' and the more established notion of 'multilingual competence'. It then moves into the domain of the foreign language classroom. It outlines studies of how much, and why, foreign language teachers have been observed to use their students' L1 (often, in the teachers' own view, excessively). It argues that attempts to exclude the students' L1 have been not only impracticable but also misguided. It proposes a framework within which teachers can avoid the dangers of using the L1 excessively but also build on its potential as a support for learning.