Sleep deprivation is considered a serious risk factor with a relevant public health impact due to its multiple effects, which we are just beginning to understand. This is underlined by the growing number of studies in recent decades that have investigated the association between sleep duration and overweight. This review gives an overview of the current state of research and potential biological mechanisms. Evidence from epidemiological studies suggests an association between short sleep duration and overweight in children as well as in adults. Different biological mechanisms have been discussed in this context with a special focus on hormonal changes as the potential mediator. To include sleep in a comprehensive strategy to prevent overweight, interventional studies that analyze the potentially protective effect of prolonged sleep duration are necessary.