Procedure
The main advantages of the PCT procedure, also referred to as the international procedure, are the possibility to delay as much as possible the national or regional procedures, and the respective fees and translation costs, and the unified filing procedure.
An international patent application (also called PCT application, as mentioned above) has two phases. The first phase is the international phase in which patent protection is pending under a single patent application filed with the patent office of a contracting state of the PCT. The second phase is the national and regional phase which follows the international phase in which rights are continued by filing necessary documents with the patent offices of separate contracting states of the PCT. A PCT application, as such, is not an actual request that a patent be granted, and it is not converted into one unless and until it enters the "national phase".
Read more about this topic: Patent Cooperation Treaty