The Patent Litigation Law Review: USA
The United States has a highly developed system of patent litigation, largely because of its historic investments in the research and development of technology, coupled with its large and profitable market for products produced both domestically and abroad. US patents are granted based on applications that are examined by the US Patent and Trademark Office (PTO).
Those patents can be enforced in the US district courts or at the US International Trade Commission if the infringing products are imported and the patent is used by a domestic industry. All US patents are subject to potential post-grant validity challenges at the PTO
Source: Law Business Research