As soon as it is granted (or 'issued') by a national patent office a patent may be legally enforced in that
territory for the term of the patent. In member countries of the World Trade Organisation the patent term is
generally 20 years from the date of filing the patent application. In exceptional circumstances extended
protection may be allowed, as with the Supplementary Protection Certificates available for pharmaceutical
inventions, due to the lengthy development and regulatory approval procedures that they must satisfy.
As a regional patent office the EPO examines and grants European Patents that may be converted into a
national patent within each of the Contracting States of the European Patent Convention. In these
countries enforcement rights for each claim of a national patent can be retroactive to the date
that the particular claim was first published in an official language of the individual country.
After the patent is granted its validity may be challenged by members of the public. The means for
doing this vary from country to country, and may involve initiating court procedings or opposing
the patent before a tribunal of the corresponding patent office.