A pivotal event in the onset of puberty in humans is the reemergence of the pulsatile release of the gonadotropin-releasing hormone (GnRH) from hypothalamic neurons. Pathways governing GnRH ontogeny and physiology have been discovered by studying animal models and humans with reproductive disorders. Recent human studies implicated the activation of kisspeptin and its cognate receptor (KISS1/KISS1R) and the inactivation of MKRN3 in the premature reactivation of GnRH secretion, causing central precocious puberty (CPP). MKRN3, an imprinted gene located on the long arm of chromosome 15, encodes makorin ring finger protein 3, which is involved in ubiquitination and cell signaling. The MKRN3 protein is derived only from RNA transcribed from the paternally inherited copy of the gene due to maternal imprinting. Currently, MKRN3 defects represent the most frequent known genetic cause of familial CPP. In this review, we explored the clinical, hormonal and genetic aspects of children with sporadic or familial CPP caused by mutations in the kisspeptin and MKRN3 systems, essential genetic factors for pubertal timing.