In the general population there is a near-normal distribution of the timing of pubertal onset, with the definitions of precocious and delayed being statistically determined (+/- 2 standard deviations, SD). Cut-off ages for Tanner genital stage G2 defining precocious and delayed puberty in boys are given. Strategies to determine key genetic determinants in the timing of puberty include large genome wide association studies (GWAS) of age-at-menarche and voice breaking in the general population, and identification of rare high-impact variants causing early, late or absent puberty in patients and their families.