Which national legal system is applied in matters of estate planning and in cross-border inheritance cases depends on different criteria. Since there is no uniform international law of succession, which law applies in the case of an inheritance must be carefully examined . This can have an impact on the right to a compulsory portion, the legal or voluntary succession and the form of wills. National tax regulations must also be taken into account.

If several legal systems are affected, a law called the „conflict of laws“ applies. The criteria for determining the applicable law are: nationality, last habitual residence, and domicile or place of property. In order to simplify matters, the European Union has defined national regulations depending on where the testator’s last habitual residence is/was. In the case of a possible inheritance with a foreign connection, the testator should take all factors into account if he or she wishes to settle his or her estate in a sensible manner.