The complex and ever-changing nature of teachers' work challenges their well-being. Teacher well-being and "fitness" includes versatility, mental strength, and commitment to promote effective teaching and learning. In framing this notion, we seek to understand the ecological influences impacting on teacher well-being and "fitness" in the twenty-first century. Drawing on the ecological theory of Bronfenbrenner, this interpretive qualitative study explored the perceptions of pre-service teachers in relation to their teacher well-being and "fitness." Data were collected from a teacher well-being survey completed by 120 final-year undergraduate pre-service teachers. The survey shed light on themes at four levels: the microsystem (individual and collective capacities); mesosystem (interrelationships between contexts); exosystem (organisational); and macrosystem (societal and legislative influences), compounded by the influence of time at the chronosystem level. These ecological influences were perceived to impact on teacher well-being and ability to be "fit" for sustained performance.