International Patent applications are separately covered under the Patent Cooperation Treaty (PCT). The PCT has two phases, Chapter I, the international phase, and Chapter II, entry into the national phase, where the applicant chooses which countries he would like to submit the patent application. This initially allows a single patent application to be searched and amended for many countries, saving the costs of multiple applications, up to 30 months after date of priority(usually the filing date of the parent application). An international application should be filed through the USPTO.
After 30 months the application is separately "entered" into countries designated by the patent owner. Each country prosecutes its separate application and grants its separate patent (and collects it own filling and renewal fees).
Typically the national phase is by country, but one exception is the European Patent Office (EPO) which allows a single PCT application to be prosecuted in Chapter II for all European Countries. Once a patent issues from the EPO it must be ratified by selected countries or "states" designated by the patent owner. Annuity fees are due annually on the EPO application. Once granted by the EPO, grant fees and translation fees are paid for each country in which the patent is maintained. Annual fees, varying by country, must be paid to keep the patents in force.