A patent is a set of exclusive rights granted by a government to an inventor or applicant for a limited amount of time (normally 20 years from the filing date). The term "patent" originates from the term to patent which means to lay open (to public inspection) and the term letters patent, which originally denoted royal decrees granting exclusive rights to certain individuals or businesses. Per the word's original definition, one theory of patent legislation is to induce the inventor to disclose knowledge for the advancement of society in exchange for a limited period of exclusivity. Therefore a patent is a monopoly right.
An application for a patent (other than a design patent) must explain how to practice (i.e., make and/or use) the invention(s) and must also include "claims" that particularly point out the invention(s). Generally, the exclusive rights are limited to the invention(s) defined by the patent's claims. Patent claims are typically of the form of a long sentence, e.g., "An apparatus for catching mice comprising, a base member for placement on a flat surface, a spring member...", "A chemical for cleaning windows comprised of 10-15% ammonia, ...", "A method for computing future life expectancies, the method comprising gathering personal data including X,Y, Z, ...", etc.
Claim language formats and practices vary widely between different countries. Each word of a claim is considered an "element" of the claim. In order to exclude someone from using your invention in a court you will have to demonstrate to the court that what the other person is using is identical to the claimed invention. (Note, while the United States is moving towards more rigid claim interpretations and generally, issued patents have a large number of claims, the practice elsewhere in the world differs.)
If an inventor takes an existing patented mouse trap design, modifies it to make an improved mouse trap, and obtains a patent on the improvement, he or she can legally build his or her improved mouse trap only with permission from the patent holder of the original mouse trap, assuming the original patent is still in force, and the patent holder of the original license has every right to deny the patent holder of the improvement use of the invention at any price. However, if the original patent owner tried to copy the inventor's improvement, he or she could sue that original patent owner to exclude him or her from using the improvement without permission.
Continuing the example though, if the inventor's improved mouse trap patent claims a guillotining member, but the original manufacturer copies other unclaimed aspects of the improvement, the inventor might not be able to exclude the manufacturer from using those other improvements.
For this reason, it is important, especially in the United States, that the patentee eventually obtain patent claims that include the absolute minimal set of items that differentiate a new invention over what came before. Dependent claims can be used to describe additional variations and features.
Procedurally, the United States system is perhaps one of the more unusual although some recent changes have brought the United States' system further into line with other major patent systems. The biggest difference that remains is that the US system awards the patent to the "first to invent", yet in the rest of the world the "first to file" is awarded the patent. In contests between different inventors over priority (called "interferences"), however, the second one to file has the burden of proof and usually loses such contests.
Patent grants are territorial in nature. Thus, patent protection in multiple countries require separate filings of patent applications in each country, or region, where protection is sought. Within Europe, a single patent application procedure is available through the European Patent Office, but successful applications result in multiple patents rather than a single European-wide patent.
Many of the international treaties are designed to afford some recognition of filing dates to patent applications filed in one country. Typically, inventors are allowed one year from the date of their filing in their home country to file the application abroad, frequently called national stage filing. Systems such as the Patent Cooperation Treaty (or PCT) allow inventors a cost effective way to further delay national stage filings.
Mathematical truths, however, are not patentable, and software inventions implementing algorithms are not patentable for this reason unless there is some kind of practical application (US law) or technical effect (European law). The US standard for the patentability of software is more liberal than that in Europe. Japanese patent law lies between the US and Europe.
Patents related to natural compounds (e.g. items found in rainforests) as well as medicines and medical treatment techniques are also controversial. There are significant country-by-country differences in handling these subject matters. For example, in the United States you can get a patent for a surgical method but you cannot enforce your right to exclude.
The comparison of the relevant prior art to the claimed invention can be highly technical in the sense that if the patent claim requires a blade to be between "5 and 10 cm" and a particular reference (one piece of literature found by the examiner) speaks of a blade having a length of "at least 11 cm", then the reference is insufficient to defeat the novelty of the claimed invention.
The threshold for the obviousness standard can be particularly frustrating in genus-species situations. For example, if an inventor finds two species of a particular genus, e.g. two particular chemical compositions out of 10,000 in the broader genus, should the inventor be entitled to a patent on the entire genus? Further, what if someone has discovered the genus already, but not isolated any of the species, are the species obvious in light of the genus? Under US law, the species may still be patentable if they produce results that are unexpectedly different than that of other previously known members of the genus.
For example, suppose a software inventor unveils the quicksort sorting algorithm to the world but only discloses it using integers (this is the species). The next day, can someone else file a patent on an "improved" quicksort suitable for use on any set where a partial ordering can be defined (this is the genus)? Under US law, this is not a question of obviousness since a claim to the genus lacks novelty as the species is known.
As TRIPS agreement declares, the term of an issued patent is twenty years from earliest claimed filing date. In the United States, for applications filed prior to June 8, 1995, the patent term is seventeen years from the issue date. For applications filed on or after June 8, 1995, the term is twenty years from the earliest claimed filing date. The rules for patents in force and pending at the transition date (June 8, 1995) are significantly more complicated but grant the patentee whichever term is longer.
Also, in several countries there are multiple types of patents, and the twenty year term frequently only applies to so called utility patents and not design, petit, or other kinds of less heavily examined patents. For example, the term of a U.S. design patent, which protects the ornamental shape of objects, lasts fourteen years from its issue date.
''In the field of industrial patents in particular we shall have seriously to examine whether the award of a monopoly privilege is really the most appropriate and effective form of reward for the kind of risk bearing which investment in scientific research involves.