The Pre-Grant Opposition by way of Representation can be filed after publication of the application (in the Patent Office Journal) till the grant of the patent by any person, in writing, against the grant of patent.
The Post Grant Opposition can be filed by any interested person within 12 months from the date of publication of the grant of patent in the Patent Office Journal at the appropriate office.

The major grounds on which the representation or opposition can be made are (a) wrongful obtainment; (b) obviousness; (c) non-patentable subject matter; and (d) anticipation having regard to the knowledge, oral or otherwise, available within any local or indigenous community in India or elsewhere.

In pre-grant opposition, the representation may be given at the appropriate office along with a statement and evidence in support of the representation. A hearing can also be requested if desired. However, the representation shall be considered only when a request for examination of the application has been filed. Upon considering the representation, if the Controller feels that the application needs amendment or rejection, a notice shall be given to the applicant in this regard. A copy of the representation may also be sent. The applicant has to reply within a period of 1 month from the date of the notice with statement and evidence in support of his application. The applicant may also request for a hearing if desired. The case shall be decided ordinarily within 1 month from the completion of above proceedings.

In post-grant opposition, the notice of opposition is to be given in the prescribed form at the appropriate office along with a written statement setting out the nature of the opponent’s interest; the facts upon which the opponent bases his case; the relief which the opponent seeks; and the evidences, if any. A copy of the statement and evidences is to be provided to the patentee.

Reply statement and evidence:
In response to the notice of opposition, the patentee can submit a reply statement setting out fully the grounds upon which the opposition is contested; and evidence, if any, in support of his case. The patentee has to reply within 2 months from the date of receipt of the copy of the written statement and opponent’s evidence by him. The patentee has to deliver a copy of his statement and evidences to the opponent.

Reply evidence by opponent:
The opponent may leave evidence in reply strictly confined to matters in the patentee’s evidence at the appropriate office. The opponent has to reply within 1 month from the date of delivery to him of a copy of the patentee’s reply statement and evidence. The opponent has to provide a copy of reply evidence to the patentee.

Hearing:
On the completion of the presentation of evidence, and on receiving the recommendation of Opposition Board, a date and time for the hearing of the opposition may be fixed, which shall be notified to the parties at least 10 days in advance. The party who desires to be heard has to inform the Controller by a notice along with the prescribed fee.

Decision:
After hearing the party or parties desirous of being heard, and after taking into consideration the recommendation of Opposition Board, the opposition shall be decided and the decision shall be notified to the parties giving reasons therefor.

On receipt of notice of opposition, the Controller constitutes an Opposition Board consisting of three members and nominates one of the members as the Chairman of Board. The Examiner who has dealt with the application for patent during the proceeding for grant of patent is not eligible as a member of the Opposition Board. The Opposition Board conducts the examination of the notice of opposition along with documents (statements and evidences) filed, and submits a report with reasons on each ground taken in the notice of opposition with its joint recommendation within 3 months from the date on which the documents were forwarded to them.