There can be no doubt that both substantive family and succession law engage in significant interaction with private international law, and, in particular, the European Union instruments in the field. While it is to be expected that substantive law heavily influences private international law instruments, it is increasingly evident that this influence can also be exerted in the reverse direction. Given that the European Union has no legislative competence in the fields of family and succession law beyond cross-border issues, this influence is indirect and, as a consequence of this indirect nature, difficult to trace.This book brings together a range of views on the reciprocal influences of substantive and private international law in the fields of family and succession law. It outlines some key elements of this interplay in selected jurisdictions and provides a basis for discussion and future work on the reciprocal influences of domestic and European law. It is essential that the choices for and within certain European instruments are made consciously and knowingly. This book therefore aims to raise awareness that these reciprocal influences exist, to stimulate academic debate and to facilitate a more open debate between European institutions and national stakeholders.