Generalized developmental psychology, including comparative psychology and national psychology; Narrow developmental psychology includes infant psychology, child psychology, juvenile psychology, youth psychology, middle-aged psychology and senile psychology.

Developmental psychology, Japanese as a developed psychology, is a branch of psychology. It mainly studies the psychological transformation in the process of human growth and development. This includes the psychological differences between children and adults, the process of children's psychological development, and how to deal with children's psychological obstacles.

In the past, scholars equated child psychology with developmental psychology, because at that time, the average life expectancy of human beings was less than 50 years old, and many people died of war or disease between the ages of 30 and 40. According to the theory of John Santrock (2004), from the point of view of psychologists at that time, the psychological development of ordinary people will not change after adulthood. So developmental psychology at that time only paid attention to children's psychological development.

However, with the extension of life span and the complexity of society, psychologists began to find that people's psychological state will continue to develop after adulthood. So we began to study the psychological development of adults and the elderly, such as the publication of Spring Training after Rain. After that, many people began to look at the psychological development of life from a holistic perspective, which has become today's lifelong development psychology.

Emile, written by JJRousseau, is recognized as the first book on children's psychology. It was a book on children's education before formal independence. Many theoretical viewpoints try to explain what development is. Among them, Piaget's development stage theory, Vygotsky's social relations theory and information processing framework theory are the most common.