In this thesis I study children's right to be heard in custody cases. The main purpose is to study the legal situation in Sweden from a European and international perspective. The emphasis given to the child’s right to be heard in cross-border custody cases in EU regulations is studied, in particular with regard to the Brussels II bis Regulation and the Charter of Fundamental Rights of the European Union, from the perspective that the child is habitually resident in Sweden. Furthermore, I study the Convention on the Rights of the Child (CRC) and the European Convention on Human Rights, both which are important rights documents in Europe. The CRC is also studied from the perspective that Sweden has incorporated the CRC as a directly applicable Swedish law as of January 1, 2020. I analyze whether Swedish law in practice is in compliance with these regulations. The conclusion is that Swedish law to some extent is, but that certain inconsistencies exist in relation to the requirements set forth in Article 12 of the CRC. In light of the study there appears to be a risk that the primacy of EU law and the principle of mutual trust can put children's rights aside. The legal situation in England, Finland and Norway regarding children's right to be heard in custody cases is studied in order to create a context in which Swedish law can be compared. The aim is to study how well children's right to be heard in custody cases is ensured in Sweden in a European comparison. It appears that the legal situation in Sweden is relatively good but that children’s right to self-determi-nation appears to be more developed in the legislation of Norway and Finland. The thesis shows some areas of improvement in Swedish law. One is the child's right to be heard in cases when the parents are able to agree on custody issues. Another is the child’s right to be heard, contrary to the parents’ wishes and without their consent. Studies show that children's actual right to express their opinion and have it regarded by the court in a custody dispute is not always ensured in practice. The conclusion is that legislative changes, or a more comprehensive consideration of Article 12 of the CRC, could lead to a better implementation in practice of the right of children to express their views and have them regarded in custody disputes.