This chapter provides a summary of the main concepts relating to how our ideas surrounding child development have developed. It covers the theoretical ideas that have influenced practice as well as providing critiques and challenges to established models. The chapter uses practical reflections to encourage the reader to question current understanding and to make appropriate links between theory and practice. The main message to take from this chapter is the importance of challenging our thinking and being open to new ideas and viewpoints when working with babies, children, and young people.