Infancy is a critical period that lays the foundation for all subsequent stages of human development. This chapter provides a comprehensive overview of developmental processes during this stage, beginning with an explanation of the stages and domains of development. It discusses the principles that govern growth and development, offering a conceptual framework for understanding how infants change and adapt across the early months of life. The chapter then examines key aspects of development during infancy, including physical and motor growth, cognitive abilities, social-emotional responses, and emerging language skills. Special attention is given to the physical and sensory characteristics of newborns, emphasizing their role in early interaction with the environment. Finally, the chapter presents major developmental milestones in infancy and underscores their significance in monitoring and supporting typical developmental progress. The special feature of the chapter is focus on the physical and sensory characteristics of newborn.