Tax residency under the treaty is based on domestic tax liability; dual residency is resolved by mutual agreement. A 'resident of a Contracting State' is any person who, under that State's laws, is liable to tax by reason of domicile, residence, place of head or main office or any similar criterion. If a person is a resident of both Contracting States under those rules, the competent authorities shall determine by mutual agreement which State will be treated as the person's residence for the Convention.