1. Ordinary Application
  2. Convention application
  3. PCT- International Application
  4. PCT -National Phase Application
  5. Application for Patent of Addition
  6. Divisional Application

Ordinary Application
The first application for patent filed in the Patent Office without claiming priority from any application or without any reference to any other application under process in the Patent office is called an ordinary application.

Convention application
When an applicant files a patent application, claiming a priority date based on the same or substantially similar application filed in one or more of the convention countries, it is called a convention application. To get a convention status, an applicant should file the application before any of the patent offices within 12 months from the date of first application in the convention country.

PCT- International Application
The Patent Cooperation Treaty or PCT is an international agreement for filing patent applications. However, there is nothing called as a 'world patent'

The PCT application does not provide for the grant of an international patent, it simply provides a streamlined process for the patent application process in many countries at the same time. Some of the benefits of the system are:

National Phase Application under PCT
The PCT-national phase must follow the international phase. The applicant must individually 'enter into the national phase'. i.e. file a National phase application in each county he wishes to enter. The applicant can enter the national phase in up to 138 countries within 30-31 months (depends on the laws of the designated countries) from the international filing date or priority date (whichever is earlier). If the applicant does not enter the national phase within the prescribed time limit, the International Application loses its effect in the designated or elected States.

Patent of Addition
Patent of addition is an application made for a patent in respect of any improvement or modification of an invention described or disclosed in the complete specification already applied for or has a patent.

In order to be patentable an improvement, should be something more than a mere workshop improvement and must independently satisfy the test of invention. The major benefit is the exemption of renewal fee so long as the main patent is renewed. A patent of addition lapses with the cessation of the main patent.

Divisional Application
A divisional application is one which has been "divided" from an existing application. The applicant, at any time before the grant of a patent can file a further application, if he so desires or if an objection is raised by the examiner on the ground that the claims disclosed in the complete specification relates to more than one invention. A divisional application can only contain subject matter in the application from which it is divided (its parent), but retains the filing and priority date of that parent. A divisional application is useful if a unity of invention objection is issued, in which case the second invention can be protected as a divisional application.