When planning to leave Poland and enter the territory of Ukraine with a car registered in Ukraine, which you are not the owner of, and the owner resides in Poland, it is advisable to have a written authorization from the car owner for the driver to cross the Polish-Ukrainian border, preferably in both directions and for a long time period to ensure the possibility of re-entering Poland by car. It is recommended that this type of authorization be drawn up in both Polish and Ukrainian. If possible, it is good to have an authorization with the owner’s signature notarized. In practice, this is the most reliable form of the document, which will be difficult for officials, Customs Officers or Border Guards to undermine. As regards the possibility of entering the territory of Ukraine with a car registered in Ukraine, which you do not own, it is best to additionally consult with the Ukrainian Border Guard.