The present chapter investigates long time trends in the adolescent fertility rate within a sample of 192 countries, highlighting the effectiveness of this demographic index in measuring reproductive healthHealth of a vulnerable group of young women. Focussing on significant variations between countries, and the potential implications for wellness of children and their family, temporal dynamics in the adolescent fertility rate reflect the evolution of socioeconomic, cultural and political factors, generating notable differences over space. The analysis also highlights the relevant contribution of initiatives of sexual educationEducation and access to healthcare services in containing adolescence pregnancy. The observed trend results in decelerated fertility dynamics in many areas, even if significant challenges persist in some countries characterized by high adolescent fertility rates. Effective policies and measure to protect adolescent reproductive healthHealth should be implemented to promote a safer and aware development path.