A patent being an exclusionary right does not, however, necessarily give the owner of the patent the right to exploit the patent.
For example, many inventions are improvements of prior inventions that may still be covered by someone else’s patent. If an inventor takes an existing, patented mouse trap design, adds a new feature to make an improved mouse trap, and obtains a patent on the improvement, he or she can only legally build his or her improved mouse trap with permission from the patent holder of the original mouse trap, assuming the original patent is still in force. On the other hand, the owner of the improved mouse trap can exclude the original patent owner from using the improvement. Some countries have “working provisions” that require the invention be exploited in the jurisdiction it covers.
Consequences of not working an invention vary from one country to another, ranging from revocation of the patent rights to the awarding of a compulsory license awarded by the courts to a party wishing to exploit a patented invention. The patentee has the opportunity to challenge the revocation of license, but is usually required to provide evidence that the reasonable requirements of the public have been met by the working of invention.