First to file (FTF) and first to invent (FTI) are legal concepts that define who has the right to the grant of a patent for an invention. Since 16 March 2013, after the USA abandoned its "first to invent/document" system, all countries operate under "first-to-file" patent priority requirement. There is an important difference between the strict nature of the FTF under the European Patent Office (EPO) and the FITF (First inventor to file) system of the United States Patent and Trademark Office (USPTO). The USPTO FITF system affords early disclosers some "grace" time before they need to file a patent, whereas the EPO does not recognise any grace period, so early disclosure under the FITF provisions is an absolute bar to later EPO patent. First to file In a first-to-file system, the right to the grant of a patent for a given invention lies with the first person to file a patent application for protection of that invention, regardless of the date of actual invention. First to disclose The concept of a grace period, under which early disclosure does not prevent the discloser from later filing and obtaining a patent, must be distinguished here from the FTI system. Germany and the UK formerly had a concept of grace period. Both FTI and grace period systems afforded the early discloser protection against later filers. The FTI system allowed non-disclosers to overturn established parties, whereas the grace system only protects early disclosers. The US moved to a grace system on 16 March 2013, which has been termed "first-to-disclose" by some writers. First to invent Canada, the Philippines, and the United States had been among the only countries to use first-to-invent systems, but each switched to first-to-file in 1989, 1998 and 2013 respectively. Invention in the U.S. is generally defined to comprise two steps: (1) conception of the invention and (2) reduction to practice of the invention. When an inventor conceives of an invention and diligently reduces the invention to practice (by filing a patent application, by practicing the invention, etc.), the inventor's date of invention will be the date of conception. Thus, provided an inventor is diligent in actually reducing an application to practice, he or she will be the first inventor and the inventor entitled to a patent, even if another files a patent application, constructively reducing the invention to practice, before the inventor. However, the first applicant to file has