At the present, patent applications filed overseas are mainly in two ways: one is the traditional "Protection of Industrial Property Paris Convention” (hereinafter referred to as the "Paris Convention") and the other is the Patent Cooperation Treaty (hereinafter referred to as the "PCT").
If you want to file applications with a number of countries (usually more than five), it is better to choose PCT, because it eliminates the trouble of filing a patent application with each country separately; else choose the Paris Convention. Where one hopes to obtain the granting of a patent as soon as possible, it is more suitable to try the Paris Convention, and where it needs to adjust in the application period, one may select the PCT.
Concerning whether a PCT patent application shall enter into the national phase of a single country, the applicant should consider many factors. For large enterprises, it needs to consider: whether and how to use the patent application in the target country's market in the future, and in addition, the anti-circumvention designed to avoid their own infringement.
For small and medium-sized enterprises, universities and individual inventors, because of the relatively high cost of the national phase and the possible need to further improve the invention, it needs to, before entering the national phase of a single country, consider whether to seek financial and technical support.
