This book offers a rich collection of international research narratives that reveal the qualities and value of peer play. It presents new understandings of peer play and relationships in chapters drawn from richly varied contexts that involve sibling play, collaborative peer play, and joint play with adults. The book explores social strategies such as cooperation, negotiation, playing with rules, expressing empathy, and sharing imaginary emotional peer play experiences. Its reconceptualization of peer play and relationships promotes new thinking on children's development in contemporary worlds. It shows how new knowledge generated about young children's play with peers illuminates how they learn and develop within and across communities, families, and educational settings in diverse cultural contexts. The book addresses issues that are relevant for parents, early years' professionals and academics, including the role of play in learning at school, the role of adults in self-initiated play, and the long-term impact of early friendships. The book makes clear how recent cultural differences involve digital, engineering and imaginary peer play. The book follows a clear line of argument highlighting  the importance of play-based learning and stress the importance of further knowledge of children's interaction in their context. This book aims to highlight the narration of peer play, mostly leaning on a sociocultural theoretical perspective, where many chapters have a cultural-historical theoretical frame and highlight children's social situation of development. Polly Björk-Willén, Linköping University, Sweden