For questions about the interaction of two or more sovereign states, including agreements and laws between them, and disputes of jurisdiction for civil or criminal matters.
Public international law is concerned with the interaction of sovereign states, and the treaties and agreements between them
Many activities today are possible only due to international treaties. International mail, international flights, and international telephone calls are possible only due to the agreements between sovereign states that allow their carriage.
Private international law is primarily concerned with the conflict of laws, and the determination of jurisdiction over a dispute between private parties.
For questions where two or more jurisdictions have an interest but the relationship between the jurisdictions is not important, please see multiple-jurisdiction.