This text proposes a model of teacher development as social, personal and professional development, and is based on the findings of a three year New Zealand research project. The project investigated the teacher development of some teachers of science working to: implement the findings of the previous Learning in Science projects; take into account students’ thinking; and base their thinking on a constructivist view of learning. The factors that helped teacher development are discussed as is a view of learning to underpin teacher development. This book is intended to be of interest to teachers, teacher educators, teacher developers, school managers and policy makers working in all curriculum areas.