There is a growing understanding and recognition of the power of children's early thinking and learning as well as a belief that science may be a particularly important domain in early childhood, serving not only to build a basis for future scientific understanding but also to build important skills and attitudes for learning. This chapter considers what we know about science learning in young children. It focuses on the importance of curiosity and making sense of the world as a natural motivation for exploration, the nature of children's early reasoning abilities and the important role played by peers and adults. With this brief background, the chapter examines the implications for practice. It proposes that effective science teaching and learning happens within the context of the developmentally appropriate classroom, a carefully designed physical environment of space and material and the selection of appropriate content. It describes a structure and approach for learning through inquiry with an emphasis on the use of practices, exploration over time, collaboration, the role of language and documentation, and integration of subject domains. The role of the teacher is considered and the chapter concludes with brief implications for needed policies.