Adolescence and puberty are highly important periods for postnatal brain maturation. During adolescence, drastic changes of neuronal architecture and function occur that concomitantly lead to distinct behavioral alterations. Unsurprisingly in view of the multitude of ongoing neurodevelopmental processes in the adolescent brain, most adult neuropsychiatric disorders have their roots exactly during this time span. Adolescence and puberty are therefore crucial developmental periods in terms of understanding the causes and mechanisms of adult mental illness. Valid animal models for adolescent behavior and neurodevelopment might offer better insights into the underlying mechanisms and help to identify specific time windows with heightened susceptibility during development. In order to increase the translational value of such models, we urgently need to define the detailed timing of adolescence and puberty in laboratory rodents. The aim of the present review is to provide a more precise delineation of the time course of these developmental periods during postnatal life in rats and mice and to discuss the impact of adolescence and related neurodevelopmental processes on the heightened susceptibility for mental disorders.