The grant of a patent invariably follows a thorough examination by expert patent examiners of the patent offices. In some jurisdictions, this grant carries with it the presumption of validity. In India, however, the validity of a patent is not guaranteed by the grant according to section 13(4) of the Patents Act, 1970. When the grant of a patent is challenged it requires evidence to prove the grounds of invalidity taken by the opponent. Most of these patent invalidity challenges, by nature of being technical, require opinions of expert witnesses.
Expert testimony in Patent litigations by DPS Parmar