Puberty is unique in the sense that its onset shows an extraordinary individual variability of about 5 years, the basis of which being still elusive despite research efforts to understand the reason why. Continuing changes in environmental influences and interaction with genetic determinants are suggested by the still evolving pattern of the pubertal process both clinically and mechanistically. For instance, secular trends towards earlier breast development have been observed during the two past decades in some countries, resulting in possible skewing of the age distribution of that pubertal sign with less obvious changes in menarcheal age. Conceptually, puberty and subsequent reproduction appear now to be influenced by conditions not only at the time when they occur, but also during fetal and perinatal life. In addition, these influences can be apparently opposing since early maturation follows fetal malnourishment and postnatal overfeeding. In this review, the semiology and pathophysiology of puberty are discussed in a lifelong developmental perspective.