Adolescence is a phase of life where transformation from childhood to adulthood takes place. Puberty, as the marker of this phase, presents a significant opportunity to lay a foundation for reproductive health of young people. Pubertal development affects female adolescents differently to their male counterparts. Within this period, the young female will experience significant changes in her body and will start her reproductive journey. It is essential that young females are prepared to ensure a smooth transition and a positive puberty experience. However, little is known about young females' knowledge of reproductive health during puberty or their sources of information about reproductive health during this critical time. Globally, research focuses on adolescents aged 15 years and above, and there is limited data on early adolescents, specifically young female adolescents age 12 to 15 years. Studies conducted with Indonesian adolescents tend to focus on sexual behaviour as a poor reproductive health outcome and fail to consider the importance of exploring adolescents' knowledge of reproductive health during puberty. This PhD study was designed to address these gaps in the literature by providing an exploration into young females' knowledge of reproductive health and the sources of information regarding reproductive health during puberty.