Pre-grant opposition is a legal challenge to the validity of a patent application filed by a third party before the grant of the patent. It is a mechanism that allows third parties to raise objections against the grant of a patent application by filing an opposition with the patent office. The pre-grant opposition system is designed to support legal certainty by allowing a pre-review of the patentability of an invention before granting the patent. In some countries, the pre-grant opposition system starts after the publication of the patent application and before substantive examination. The opponent shall state the grounds for opposition and submit any evidence. If no opposition is filed during the prescribed time period, the patent will be granted. The pre-grant opposition mechanism is an essential safeguard in Indian patent law. It is an opportunity for third parties to challenge the validity of a patent application and prevent unmerited monopolies.