In this first part of the book, we present our task – to empirically study and theorize teaching (and, in extension, didaktik) as an activity responsive to play and the tradition and practices of preschool (early childhood education and care, ECEC) – and some premises of our approach (Chaps. 1 and 2). In Chap. 3, we review key research and theorizing on play in early childhood education. In the final chapter of this part of the book, Chap. 4, we present our way or working in terms of what we refer to as a combined research and development project.