Infertility affects an estimated 80 million individuals worldwide, or 10–15% of couples of reproductive age. The number of assisted reproductive technology (ART) cycles in the United States more than doubled between 2000 and 2013. In 2015, about 1.7% of all live births in the United States were the result of this technology. In the US, studies of the long-term outcomes of ART involve the challenge of linking databases, in which one database has information on the treatment parameters, and the other database captures the outcomes of interest. This chapter discusses the linkage efforts, methodologies, and resulting research in the US by the Society for Assisted Reproductive Technology (SART) and the Centers for Disease Control and Prevention (CDC), and the health linkages routinely performed in the Nordic countries. Strengths and limitations of these approaches are also discussed.