An analysis of the relationships between teacher unions and governments sheds light on teacher union leadership, what drives it and what ethos lies behind it, illuminating the connections between such initiatives and developing theory in the role of teacher unions. Teacher union leadership in turn enables and encourages teachers to exercise leadership in their own and others' learning, in supporting learning and in influencing policy. This paper explores the potential for teacher unions to take the lead in supporting teachers to develop what has become known as teacher policy--an overarching term that encompasses policies on pedagogy, professional development, standards and evaluation, and on improving teacher involvement in research on classroom practice, and school improvement. Learning, in all its manifestations, lies at the heart of teacher policy. While its primary focus is on pupil learning, this is necessarily reliant on professional learning and on how that impacts on and shapes policy--at school and local authority level, at national level and, in specific instances, in respect of international teacher policy. This paper concludes that the withdrawal by many governments from the direct oversight of teacher policy and, in particular the provision of teachers' professional development, while creating significant challenges for the teaching profession, presents new opportunities for teacher unions to take the lead on behalf of their members and fill this vacuum.