Book excerpt: This book introduces readers to the principles of a fairly new branch of psychology – positive psychology – and demonstrates how they can be applied in the context of second language acquisition in a natural environment and in instructed foreign language (FL) learning. It focuses both on the well-being and success of the learner and the professional and personal well-being of the teacher. Further, the book stresses the importance of the positive emotions and character strengths of those involved in the process of language learning and teaching, as well as the significant role played by enabling institutions such as school and, at the micro-level, individual FL classes.