Environmental education, both in and outside of the classroom, aims to facilitate adoption of sustainable practice by both school students and the general public. This paper explores the role of free-choice learning experiences in this regard. An overview of theoretical approaches underpinning free-choice learning research is provided, examples are presented of the ways in which informal educational settings can promote environmentally sustainable attitudes and behaviour, and the factors contributing to the effectiveness of these endeavours are discussed. By reviewing research evidence in relation to these issues, the paper identifies the current 'state of the game' and areas where new research is needed.