If a parent abducts a child to a country that is a signatory to the Hague Convention on Civil Aspects of Child Abduction there are five main defenses to a return petition:
1) the existence of a grave risk that return would expose the child to physical or psychological harm or otherwise place the child in an intolerable situation.
2) the child objects to return and is of sufficient age and maturity to appropriately consider the objection;
3) the petitioner was not acually exercising custody rights at the time of the removal or retention;
4) more than a year has elapsed from the date of the wrongful removal or retention until the commencement of the judicial proceeding seeking an order of return, and the child is now settled in 5) the new environment, or
the return would not be permitted by the fundamental principles of the requested state relating to the protection of human rights and fundamental freedoms (the Article 20 defense).

In the United States the grave risk of harm and the Article 20 defenses must be established by the legal standard of Clear and Convincing Evidence.