This paper is set in the context where there is a policy emphasis on teacher learning and development in a number of countries as a means towards school improvement. It reports on a longitudinal research project about the workplace learning of English secondary school teachers, carried out between 2000 and 2003. This was part of a Teaching and Learning Research Programme network of projects looking at learning in a variety of workplaces. The paper contrasts some key features in the teacher development and workplace learning literatures, which highlight different understandings of learning--as acquisition, participation and/or construction. We argue that insights from the literature and the research, including insights from other projects in the network, enhance our understanding of teacher learning. The paper describes some of the main ways in which experienced teachers learn, and then identifies three dimensions which interact in influencing the nature of that learning. The dimensions are: the dispositions of the individual teacher; the practices and cultures of the subject departments; and the management and regulatory frameworks, at school and national policy levels. Based upon the findings, we argue that current policy approaches to teacher development in the UK are over-focused on the acquisition of measurable learning outcomes, short-term gains, and priorities that are external to the teachers. They also assume and strive for impossible and counterproductive universality of approach. Instead, our findings suggest that teacher learning is best improved through a strategy that increases learning opportunities, and enhances the likelihood that teaches will want to take up those opportunities. This can be done through the construction of more expansive learning environments for teachers. We examine briefly some barriers to this approach, and give some suggestions of what could be done.