The Protocol Relating to the Status of Refugees is a key treaty in international refugee law. It entered into force on 4 October 1967, and 146 countries are parties. The 1951 United Nations Convention Relating to the Status of Refugees restricted refugee status to those whose circumstances had come about "as a result of events occurring before 1 January 1951", as well as giving states party to the convention the option of interpreting this as "events occurring in Europe" or "events occurring in Europe or elsewhere".