This thesis reports on a practitioner research study which adopts a social constructivist approach (Williams and Burden 1997) to the investigation of classroom motivation. The social constructivist approach to motivation shows its strength in taking into account both the internal and external factors of motivation influences. It places its emphasis on the effect of contextual factors on learner motivation and it considers motivation to be constructed through learners’ interaction with the learning context. Taking into account the notion of social constructivism, this practitioner research study aims to explore how classroom motivation is co-constructed through the social interaction between teachers and learners. The study took place in two English courses for non-English majors in a Taiwanese university for one semester (February 2008—June 2008). Classroom motivation is investigated through a variety of research methods. Both qualitative and quantitative research instruments—questionnaires, learner reflective diaries, post-class reflective writings, learner interviews and teaching journals—were used in an attempt to explore how classroom motivation develops in cycles, in which teachers and learners receive reciprocal effects from each other. The results of the study shed light on how different types of teacher and learner behaviours influence learner and teacher motivation respectively.