According to different estimates, each year up to 15 million patients worldwide cross national borders to seek medical treatment. For many, reproductive travel offers the only opportunity to receive health services, which are unaffordable, unavailable, or illegal in their home countries. These patients include gay couples or single women, who are not eligible for fertility treatment, or persons who have restricted access to abortion services. The rapid expansion of cross-border reproductive services poses serious challenges. While specific international norms governing cross-border healthcare remain scarce, many non-state actors, including medical associations, assume regulatory and law-making functions. Consequently, the multiple sets of overlapping rules concerning medical liability, parenthood, or citizenship are often impenetrable. Patients often find themselves in extremely vulnerable legal positions, without sufficient remedy and appropriate legal protection. This article offers a new lens to analyse the processes that shape transnational reproductive health law (TRHL). It suggests that scholars should focus on developing a coherent conceptual framework that captures not only the traditional 'top-down' law-making processes, such as international law making and diffusion, but also the horizontal and bottom-up formation of transnational reproductive health law. It suggests that future research should examine how TRHL is slowly and latently developing a constitutional order comprising common rules and higher-ranked norms, which are formed at the national, supranational, and international level across the globe. The article focuses on abortion and assisted reproduction as the two most representative and contentious aspects of TRHL. It is different from a typical academic article in that it has a programmatic character. It focuses primarily on setting out a detailed intellectual agenda that can help reimagine the role and nature of transnational health law in the future.