Firstly, essential developmental aspects of the focused periods of life, namely childhood and adolescence, are discussed. Furthermore, different issues of overweight and obesity in childhood and adolescence are highlighted. Besides the definition and the assessment, possibilities of classification and epidemiological aspects are of interest. Physical and psychiatric consequences, which can be associated with obesity are also presented. In the context of a model of multifactorial genesis of obesity, different causing and maintaining factors are described. In addition to genetic and biological risk factors, the significance of several psychosocial factors is illustrated. Finally, the focus is on the therapy of obesity in childhood and adolescence.