In a patent or patent application, the claims define, in technical terms, the extent of the protection conferred by a patent, or the protection sought in a patent application. The claims are of the utmost importance both during prosecution and litigation.
For instance, a claim could read:
- "An apparatus for catching mice, said apparatus comprising a base, a spring member coupled to the base, and ..."
- "A chemical composition for cleaning windows, said composition substantially consisting of 10–15% ammonia, ..."
- "Method for computing future life expectancies, said method comprising gathering data including X, Y, Z, analyzing the data, comparing the analyzed data results..."
In most jurisdictions, a patent is a right to exclude others from making, using, importing, selling or offering for sale the subject matter defined by the claims when the claim is for a thing (apparatus, composition of matter, system, etc.). If a claim is for a method, the right to exclude would be to exclude any single party from carrying out all the steps of the claim. In order to exclude someone from using a patented invention in a court, the patent owner, or patentee, needs to demonstrate that what the other person is using falls within the scope of a claim of the patent. Therefore, it is more valuable to obtain claims that include the minimal set of limitations that differentiate an invention over what came before, i.e. the so-called prior art. On the other hand, the fewer the limitations in a claim, the more likely it is that the claim will cover or "read on" what came before and be rejected during examination or found to be invalid at a later time for lack of novelty or obviousness.
Patents have not always contained claims. In many European countries, patents did not contain claims before the 1970s. It was then often difficult to decide whether a product infringed a patent, since the sole basis to know the extent of protection was the description, in view of the prior art. Claims have been necessary parts of U.S. patent applications since the enactment of the Patent Act of 1836.
However, even among patent legal systems in which the claims are used as the reference to decide the scope of protection conferred by a patent, the way the claims are used may vary substantially. Traditionally, two types of claiming system exist:
- the "central claiming system", according to which the claims identify the "centre" of the patented invention. The exact scope of the protection depends on the actual nature of the inventor’s contribution to the art in the concerned technology.
- the "peripheral claiming system", according to which the claims identify the exact periphery, or boundary, of the conferred protection. In this system, the burden of drafting good claims is much higher on the patent applicant (or on his counsel). The applicant receives the protection he or she requested and almost nothing more, provided that the invention is new and non-obvious. This theoretically makes it easier for third parties to examine whether infringement may exist or not.
No patent system today is a purely either central or peripheral, but the system used in Germany and most of the other countries of continental Europe is considered more central than the system currently used in the United Kingdom, the United States, and especially Japan, which are more peripheral. In recent years, Japan's system has become more peripheral, while the system used in the United States has become less peripheral.[dubious ]
Requirements and structure 
In most modern patent laws, patent applications must have at least one claim, which are critical defining elements of the patent and the primary subject of examination. In some patent laws however, a date of filing may be obtained for an application which does not contain any claim.
European Patent Convention 
Under the European Patent Convention (EPC), a claim must define the matter for which the protection is sought in terms of technical features. These technical features can be either structural (e.g. a nail, a rivet) or functional (e.g. fastening means).
Regarding the structure of a claim, under the European Patent Convention, what is called the "preamble" is different from the meaning the "preamble" has under U.S. patent law. In an independent claim in Europe, the preamble is everything which precedes the expression "characterized in that" or "characterized by" in a claim written according to the so-called "two-part form", and therefore everything which is regarded as known in combination within one prior art document, namely the closest prior art document. For this reason, in Europe, the preamble of a claim is sometimes also called "pre-characterizing portion".
United States 
A claim may include the following parts:
- A preamble that recites the class of the invention, and optionally its primary properties, purpose, or field: "An apparatus..." "A therapeutic method for treating cancer..." "A composition having an affinity for protein X..." This preamble may also reference another claim and refine it, e.g., "The method of claim 1..." (See "dependent claim" below.).
- A "transitional" phrase that characterizes the elements that follow. The phrases "comprising", "containing" and "including" are most often used and (under some patent laws, specifically US) preferable, as it means "having at least the following elements..." and are therefore open (inclusive) and do not exclude additional limitations. The phrases "consisting of" and "consisting essentially of" are (under some patent laws, specifically US) more limiting, as they mean "having all and only" or "virtually only" and are therefore closed (exclusive). In the US, the phrase "consisting of" excludes additional limitations, while the phrase "consisting essentially of" excludes additional limitations that would "materially affect the basic and novel characteristic(s) of the claimed invention".
- A set of "limitations" that together describe the invention: "an X, a Y, and a Z connected to the X and the Y." The elements should be described as though they interact or cooperate to achieve the desired result. The distinction between elements and limitations is explained in the article All elements test.
- Optionally, a purpose clause that further describes the overall operation of the invention, or the goal that the invention achieves ("wherein the Z simultaneously controls the X and Y," or "wherein the Z accomplishes purpose W by controlling X and Y," etc.)
Interpretation or claim construction 
The claims often use precise language. Certain words commonly used in claims have specific legal meanings determined by one or more court decisions. These meanings may be different from common usage. For instance, the word "comprises", when used in the claims of a United States patent, means "consists at least of". By contrast, the word "consists" means "consists only of", which will lead to a very different scope of protection.
Furthermore, in U.S. patent practice at least, inventors may "act as their own lexicographer" in a patent application. That means that an inventor may give a common word or phrase a meaning that is very specific and different from the normal definition of said word or phrase. Thus a claim must be interpreted in light of the definitions provided in the specification of a patent. The specification of a patent is a written description of how to make and use the invention (see also: sufficiency of disclosure). In U.S. law, a claim is interpreted in a Markman hearing. The Public Patent Foundation has constructed Free Claim Construction Dictionaries.
- Construction, whether of a patent or any other document, is of course not directly concerned with what the author meant to say. There is no window into the mind of the patentee or the author of any other document. Construction is objective in the sense that it is concerned with what a reasonable person to whom the utterance was addressed would have understood the author to be using the words to mean. Notice, however, that it is not, as is sometimes said, "the meaning of the words the author used", but rather what the notional addressee would have understood the author to mean by using those words. The meaning of words is a matter of convention, governed by rules, which can be found in dictionaries and grammars. What the author would have been understood to mean by using those words is not simply a matter of rules. It is highly sensitive to the context of and background to the particular utterance. It depends not only upon the words the author has chosen but also upon the identity of the audience he is taken to have been addressing and the knowledge and assumptions which one attributes to that audience.
Basic types and categories 
||The examples and perspective in this article may not represent a worldwide view of the subject. (December 2010)|
There are two basic types of claims:
- the independent claims, which stand on their own, and
- the dependent claims, which depend on a single claim or on several claims and generally express particular embodiments as fall-back positions.
The expressions "in one embodiment", "in a preferred embodiment", "in a particular embodiment", "in an advantageous embodiment" or the like often appear in the description of patent applications and are used to introduce a particular implementation or method of carrying out the invention. These various embodiments may or may not each be claimed with specificity. They might serve as multiple examples of a more general "genus" that is claimed. In some cases the examiner might declare that what the applicant presented as variations of one invention are actually separate invention that need to be examined individually.
Some claims are "stand alone" independent claims, not referring back to any earlier claim. Other are dependent claims that do refer back to an earlier claim, take on all of the limitations of that claim and then add additional restrictions. e.g. "The handle of claim 2 where it is hinged." Each dependent claim is, by law, more narrow than the independent claim upon which it depends. Although this results in narrowed coverage than provided by the independent claim which it depends from, it is additional coverage and there are many advantages to the patent applicant in submitting and obtaining a full suite of dependent claims:
- Clarification of the independent claim language: Independent claims are typically written with very broad terms, to avoid permitting competitors to circumvent the claim by altering some aspect of the basic design. But when a broad wording is used, it may raise a question as to the scope of the term itself. For example, does a "base" include a "set of legs"? A dependent claim, including the phrase, "wherein said base comprises a set of legs," if allowed by the patent examiner, clarifies that the word base in the independent claim does not necessarily include legs. This is by the logic of claim differentiation. In the U.S, at least, each claim in an issued patent is presumed to cover different territory than any other claim. If in claim 2 the base must include legs, then the wording of claim 1 must not be taken as requiring the base to include legs. In practice, dependent claims are often used to home in on the inventor's preferred embodiment of the invention (e.g., the actual product design that the inventor intends to use.) The independent claim broadly describes the invention; dependent claim #1 describes the invention in a narrower aspect that more specifically describes the preferred embodiment; dependent claim #2 is narrower still; etc.
- Possible invalidity of base claim: It is impossible to know, when beginning the application process and even at the time of patent issuance, if a patent claim is valid. This is because any publication dated before the application's priority date and published anywhere in any language can invalidate the claim (excluding publications by the inventor published during the grace period in certain countries such as U.S., Canada and Japan). Furthermore, even applications that were not yet published at the time of filling, but have a priority date prior to the priority date of the application, can also invalidate the claim. As it is impossible to gain an absolute and complete knowledge of every publication on earth, not to mention unpublished patent applications, there is always some degree of uncertainty. If the independent claim is determined to be invalid, however, a dependent claim may nevertheless survive, and may still be broad enough to bar competitors from valuable commercial territory.
- Claim differentiation: In United States patent law, under the doctrine of claim differentiation, each claim is presumed to cover a different aspect of the invention than in each other claim. This doctrine may be relied upon to help maintain broad claim scope in the case where a claim standing alone might be construed as having either a broad or a narrow interpretation. If a dependent claim is added that depends from this "parent" claim but is specifically drawn to the narrower interpretation, then the parent claim must necessarily be different - i.e., it must be the broader interpretation. As construed in the courts, the doctrine of claim differentiation dictates that it "is improper for courts to read into an independent claim a limitation explicitly set forth in another claim."Environmental Designs Ltd. v. Union Oil Co. of California, 713 F.2d 693, 699 (Fed. Cir. 1984). This means that if an independent claim recites a chair with a plurality of legs, and a dependent claim depending from the independent recites a chair with 4 legs, the independent claim is not limited to what is recited in the dependent claim. The dependent claim protects chairs with 4 legs, and the independent claim protects chairs with 4 legs as well as chairs having 2, 3, 5 or more legs.
Under the European Patent Convention, when a claim in one particular category (see below), e.g. a process claim, depends on a claim from a different category, e.g. a product claim, it is not considered to be a dependent claim but an independent claim. Under U.S. law, this is still counted as a dependent claim, regardless of the class change.
The rules of claim drafting also permit "multiple dependent claims" that reference more than one other claim, e.g.: "3. Method of claim 1 or 2, further comprising..." The rules for this are quite specific: specific claims must be referenced ("the method of any of these other claims" is incorrect); the claims must be referenced in the alternative ("the method of claims 1 and 2" is incorrect); etc. While still acceptable, this claim style is seldom used in the U.S. because it is counted for filing fee purposes according to the number of claims that it references. Thus, if the claim depends from three former claims, it is counted for fee purposes as three dependent claims. In light of the "excess claim" fees currently imposed by the USPTO, this tactic can quickly become expensive. Multiple dependent claims are, however, very commonly used in other jurisdictions, including Canada and Europe.
Claims can also be classified in categories, i.e. in terms of what they claim. A claim can refer to
- a physical entity, i.e. a product (or material) or an apparatus (or device, system, article, ...). The claim is then called respectively "product claim" or "apparatus claim"; or
- an activity, i.e. a process (or method) or a use. The claim is then called respectively "process claim" (or method claim) or "use claim".
Special types of claims 
In addition to the above basic claim types, there are also many special types of claim which are used in different circumstances. Sometimes a particular claim form is required by law if a patent is to be granted for a particular invention, such as for a second medical use of a known substance where the "Swiss-type" claim might be required. Another reason to use a particular claim might be to catch a particular class of infringer.
See also 
- Catnic Components Ltd. v. Hill & Smith Ltd. (1982)
- Claims under the European Patent Convention
- Clearance search and opinion
- Doctrine of equivalents
- Probatio diabolica, in relation to product-by-process claims
- Patent Act of 1836, Ch. 357, 5 Stat. 117 (July 4, 1836)
- See Decision of Supreme Court of Japan (Saikou Saibansho), February 24, 1998 Case No. Heisei 6 (o) 10831No. Heisei 6 (o) 1083, first recognizing the doctrine of equivalents.
- See Warner-Jenkinson v. Hilton Davis, 520 U.S. 17 (Fed. Cir. 1997) (restricting the scope of the doctrine of equivalents.)
- See for instance Article 11(1) PCT.
- Article 84 EPC, Rule 43(1) EPC
- Guidelines for Examination in the EPO, section f.iv.2.1 : "Technical features."
- Rule 43(1) EPC (previously Rule 29(1) EPC 1973) and, for instance, EPO board of appeal Decision T 13/84, Headnote 1.
- See for instance "The pre-characterising portion of the claim is based on..." in Decision T 0443/11 of 30 January 2012, item 2.1.
- USPTO MPEP 2111.03
- Google Books Jeffrey G. Sheldon, How To Write a Patent Application sec. 188.8.131.52 (1992); see American Choc. Mach. Co. v. Helmstetter, 142 Fed. 978, 980 (2d Cir. 1905) ("The distinction between a combination and an aggregation lies in the presence or absence of mutuality of action. To constitute a combination it is essential that there should be some joint operation performed by its elements, producing a result due to their joint and co-operating action, while in an aggregation there is a mere adding together of separate contributions, each operating independently of the other. Defendant's machine comprises merely an aggregation of two devices. There is no mechanical or functional mutuality of operation. It is not a combination because there is no co-operation between the coating and jarring mechanisms, because the two devices do not unitedly perform their functions, and because they are not necessarily combined in one machine, and do not act together to secure the final result.") (citations omitted).
- UK House of Lords, Kirin-Amgen Inc & Ors v Hoechst Marion Roussel Ltd & Ors  UKHL 46 (21 October 2004) (paragraph 32)
- "embodiment = a specific, disclosed example of how an inventive concept, that is more generally stated elsewhere in the disclosure, can be put into practice." in WIPO, International patent classification (Version 2009), Guide, page 33.
- Rule 43(4) EPC
- Guidelines for Examination in the EPO, section f.iv.3.4 : "Independent and dependent claims": "(...) a dependent claim may refer back to one or more independent claims, to one or more dependent claims, or to both independent and dependent claims."
Further reading 
- The construction of product-by-process claims, 11th European Patent Judges' Symposium, Copenhagen, Official Journal of the EPO 2003, Special Edition, No. 2, p. 20-75 (pdf)
- European Patent Convention
- US patent law (Title 35 of the US Code)
- Studies on patent claims
- When small is beautiful: measuring the evolution and consequences of the voluminosity of patent applications at the EPO This paper addresses issues in measuring the voluminosity of patent applications (number of claims and pages) and highlights patterns in its evolution.