This article provides theoretical perspectives on continuing professional development (CPD, henceforth) and in-service teacher education and training (INSET, henceforth). Regarding good practice in INSET and CPD for English language teachers, implications are drawn from the review of international practice in different situations. The first is to recognize the unique context each school has; there cannot be a ‘one size fits all’ policy for every school in a given system. Not imposed by outsiders on teachers, successful professional development and change should start with the English teacher and the acknowledgement of his or her agency. At the heart of professional development is English teachers’ willingness to open up their practice to public scrutiny. The review of the literature suggests that information technology has enabled online professional communities to be established amongst diverse school contexts across geographical boundaries. A collaborative professional learning environment for English language teachers is recognized as a critical component in the success of CPD and INSET. It is suggested that educational systems should provide the conditions fostering such professional learning environments for the benefit of both English teachers and their pupils.