Wellbeing is at the heart of a life well lived. Our emotions, health and general satisfaction dictate whether we flourish or flounder. In life more generally, and language education specifically, wellbeing should be centre stage and the fundamental foundation on which everything else is built. Teachers should be flourishing in their schools and professional roles, as should learners. In a class defined by positive wellbeing, everyone benefits – teachers are less at risk of burnout and tend to teach more creatively, and learners are typically more motivated and have higher levels of achievement. In this talk, I focus on the criticality of wellbeing, showing how and in what ways it impacts language learning and teaching. In particular, I show how teacher and learner wellbeing are interconnected through social relationships and processes of contagion with each impacting the other. As positive relationships are one of the defining pillars of wellbeing, we consider in more detail what the qualities of positive relationships are and how teachers and learners can improve their skills of relating to each other. We also reflect on data from a range of studies investigating teacher wellbeing and consider other key social and individual factors that contribute to teachers flourishing in their professional roles, which also impacts positively on learner wellbeing.