Play lies at the heart of preschool pedagogy. It has been so since the advent of this institution, built on the ideas of scholars such as Friedrich Fröbel, Jean-Jacques Rousseau and John Dewey. The history of play in preschool, in the twenty-first century, could be described in terms of shifting perspectives (Cutter-Mackenzie, Edwards, Moore, & Boyd, 2014). These are interesting to consider as they create the backcloth for the aim of the research project reported in the present book. At the time when the first preschools were established, the value of play in childhood was ideologically stated as something essential. Rousseau launched the image of the innocent, naturally evolving child needing protection from adults to be able to play, interact with nature and in this way, be in the process of 'natural learning' (Cutter-Mackenzie et al., 2014; see also Loizou, 2017). This image has paved the way for the child-centeredness that still is a hallmark of preschool practice. Subsequently, Piaget, the preeminent and for a long time dominating developmental psychologist, further strengthened the view of children discovering the world through unassisted exploration and play. Developmental psychology became the "research evidence base for protecting children's opportunity to learn and develop through the provision of traditionally valued play-based experience" (Cutter-Mackenzie et al., 2014, p. 16). However, eventually critical voices started to problematize the 'what' of learning; children might learn through play, but what do they learn? In line with such discussions, adults' role in children's play has come to the fore as a debated issue, including whether the 'intervention' of adults in children's play are necessary to support 'appropriate learning' (and what is considered 'appropriate' and according to whom or what criteria), or whether such 'intervention' damage children's sense and development of agency. Today, Cutter-Mackenzie and colleagues (ibid.) argue, what dominates discussions about early childhood education is what they refer to as the post-developmental perspectives. These are characterised by an emphasis on social and cultural aspects on learning and human cognition, and also on the sociology of childhood. The interest in how and why play is used in preschool has increased, and, for example, how peer cultures take form among children (e.g., Corsaro, 2011). The work of the