The 2030 Agenda for SustainableDevelopment’s Goal for Gender Equality (SDG5 to: AchieveGender Equality and Empower Women and Girls) sets a seriesof ambitious targets that will measure progress towardsattaining this goal. One such target is to: ‘eliminate allharmful practices, such as child, early and forced marriageand female genital mutilation. In this paper we examine howefforts to achieve legal identity for all, including birthregistration for all, can contribute to ending childmarriage. The authors begin by setting out the currentcontext presenting data on child marriage and its impactsand then turn to birth registration drawing out its linkswith fundamental human rights and development goals. We thenpresent estimates of the numbers of unregistered children inthe world’s global regions based on the World BankIdentification for Development Initiative (ID4D) dataset.The authors turn next to the link between birth registrationand child marriage rates6 using data on birth registrationin the 106 countries for which authors also have data onchild marriage. The authors find a correlation between highbirth registration rates and low child marriage rates anddiscuss this link in the context of evidence on theunderlying causes and drivers of child marriage. The authorsexplore the links between birth registration and childmarriage in greater depth in two case studies: the first oneexamines the role of identity papers, particularly birth andmarriage certificates, in the enforcement of minimum age ofmarriage laws for Syrian refugees in Jordan; the second onediscusses how a recently adopted strategy to streamline theprocess for obtaining birth certificates in Indonesia cancontribute to reducing child marriage. Despite evidence of acorrelation, however, a policy pursuing universal birthregistration is unlikely to have impact on child marriagerates unless it is embedded in broader efforts to end childmarriage, including legal reform, advocacy, and national andlocal policies and programs which work with communities tochange social norms and are designed to reach people thatare at risk from being excluded from national efforts, forexample refugees and internally displaced peoples.