In this chapter, we explain the premise of the book by setting out the argument that a routine part of teachers’ work is to design learning experiences for their students. Throughout their careers, teachers develop extensive professional knowledge that equips them to consider and balance many factors when designing lessons, activities, and programs to meet the diverse needs particular to their group of students. While recent research in this area demonstrates that teachers engage in design in ways similar to other better-understood design professionals such as architects and engineers, this way of understanding how teachers think about and undertake their work is relatively new. By understanding teachers’ design work we can better support them to become more effective designers of learning experiences, the outcomes of which have the potential to significantly improve the quality of education for all students. In providing the background to the book, we present the evolution of the concept of ‘teacher as learning designer’ across several strands of inquiry organised around learning design and design thinking. We set out the idea of ‘teacher as designer’, where it comes from and how it has developed over time. The chapter ends with an overview of the book structure and focus of each chapter.