One of the aims of the Private International Law is to determine the law applicable to a matter of private law with an international element. In the connection with this main idea, this chapter deals with and tries to answer these questions: Whether a duty to apply the conflict-of-law rule arises when tackling the question with an international element; Whether a duty to apply foreign law arises when the conflict-of-law rule refers to it; The nature of such foreign law – whether it has legal or factual nature; Once directed to apply the foreign law, whether it is possible to avoid it and refuse to apply it; Whether there is a duty to know or at least to become acquainted with such foreign law; In what manner the foreign law should be applied, including the issues of interpretation and intertemporal law; What is the scope of application of the foreign law, i.e. whether to take into account the conflict-of-law rules of the lex causae or the overriding mandatory rules; Whether a party is entitled to appeal when foreign law is applied erroneously.