Comprehensive sexuality education (CSE) has strong support in the international discourse, and is supported by a relatively robust evidence base. In general, the evidence suggests that CSE has positive impacts on behaviour change, such as increased condom use, girls’ empowerment and delayed sexual debut. This is achieved through increasing knowledge and changing attitudes. There is strong evidence to support the effectiveness of CSE programmes in these areas. However, there is less evidence on whether CSE can change biological indicators, notably incidences of STIs, including HIV, and pregnancies. The literature highlights that this is an area of research which needs more conclusive findings.