Prior Use Right says that if a you have used a technology commercially for more than a year prior to the file date of a patent[1], or public disclosure thereof

Prior Use Right says that if a you have used a technology commercially for more than a year prior to the file date of a patent[1], or public disclosure thereof if your technology is a derivative of the that disclosure, you cannot be held in violation of the patent. This holds regardless of if you have publicly disclosed your use of this technology or not. When you combine this with Trade Secret law you protect yourself from one of your employees taking your technology, starting a new company and patenting it (potentially coming in under the 1 year mark). First-to-File only comes into play when multiple entities file for overlapping patents, it simply finds in favor of the first to file for a provisional patent. This avoids a mess of trying to determined who came up with the idea first, which was always a contest of who documented first. [1] You could still be in violation and not know it as provisional patents are non publicly disclosed for 18 months, so in reality there is technically a 2.5 year window where you can't be absolutely sure someone else has filed.