Where validity challenges come from
Most challenges rest on prior art, meaning earlier patents, publications, products, or public uses showing that the claimed invention was already known or would have been obvious. Others go to the patent itself, arguing for example that it claims an abstract idea or that its claims do not clearly define their scope. A patent issued by the USPTO is presumed valid in court, and the challenger carries a heavy burden there. Examiners work under time pressure and may not have seen the most relevant references, which is why searching after issuance often turns up new art.
Choosing a forum
In district court, validity is usually raised as a defense or counterclaim to infringement. At the USPTO, inter partes review before the Patent Trial and Appeal Board considers novelty and obviousness based on earlier patents and printed publications, under a lower burden than in court, but the office decides whether to institute a review and has used that discretion more actively at times. Ex parte reexamination is another office route, less adversarial and with little participation by the challenger. A challenger who loses an inter partes review may be barred from raising the same grounds later. Patent owners should expect their prosecution history and statements about claim meaning to be tested in each forum.
Opinions and preparation
Companies launching a product near an existing patent sometimes obtain a written opinion of counsel on validity or non-infringement, which can bear on willfulness if a dispute arises later. Patent owners preparing to assert a patent often review its validity first, so the other side's search does not produce the first surprise. Either way, we begin with the claims, the file history, and a prior art search focused on the features that matter commercially. Bring the patent number, any letters exchanged, the products involved, and any art you already know about.
