The impact from computers software on teaching and students' learning of mathematics has been offered increasingly attention in educational research. This book reports from a study of teachers' first ever use of a dynamic geometry software, Cabri, in teaching at lower secondary schools in Norway. The study was situated within developmental projects where teachers and university educators worked together for several years. The book gives a characterisation of teachers' progression through a development process in which they implemented and orchestrated Cabri-use in their teaching. The book provides a contribution to policy makers and research in mathematics teaching, and suggests implications for mathematics teachers considering implementation and orchestration of dynamic geometry software-use in teaching. Conclusions are presented indicating that implementation of a new computer software tool can offer teachers a medium to develop new styles of mathematics teaching. Implications are suggested concerning future developmental projects aiming to support sustainable development in mathematics teaching.