Pubertal development is the last phase of a continuum of changing gonadotrophin releasing hormone (GnRH) activities. Whether or not puberty tends to start at a younger age, as has been recently described in a population of black Americans, remains under debate. Such early onset has not been confirmed in different European countries. Ideas about the underlying mechanisms responsible for the reawakening of GnRH release at the onset of puberty have changed significantly during the last decades. At this moment, the common opinion is that neuronal outgrowth of both GnRH and other regulatory neurons results in changing interactions and activities. Sex steroids, as well as various central neurotransmitters, play a role in modulating GnRH release. Active release after birth is followed by the restraint of childhood. A re-onset of GnRH excitatory activities heralds the onset of puberty. This chapter gives an overview of the many factors involved.