Doctrine of equivalents
Prosecution history estoppel


According to the European Patent Convention (EPC) and its Protocol on Interpretation, patent claims should be interpreted by adopting a balanced approach that combines fair protection for the patent holder with a reasonable degree of certainty for third parties.

Claims should therefore not be interpreted strictly – that is, by considering only the dictionary definition of a certain term. However, claims should not be treated as mere guidelines either, since they play a determinative part in deciding the patent's scope. The Protocol requires a middle ground between the two extremes.

Doctrine of equivalents

For the purpose of determining the extent of protection conferred by a European patent, the Protocol further requires that due account must be taken of any element that is equivalent to an element specified in the claims. This is the so-called "doctrine of equivalents". This doctrine can be used by the patentee to claim a broader scope of protection in infringement proceedings.

However, no definition of "equivalents" is given in the EPC or the Protocol. The World Intellectual Property Organization (WIPO) proposed the following definition in its Treaty Supplementing the Paris Convention as far as Patents are Concerned (1991):

An element ("the equivalent element") shall generally be considered as being equivalent to an element as expressed in a claim if, at the time of any alleged infringement, either of the following conditions is fulfilled in regard to the invention as claimed:

  1. the equivalent element performs substantially the same function in substantially the same way and produces substantially the same result as the element as expressed in the claim, or
  2. it is obvious to a person skilled in the art that the same result as that achieved by means of the element as expressed in the claim can be achieved by means of the equivalent element.

It is therefore clear that the scope of protection of a patent claim can be extended beyond the literal wording of the claims through the application of the doctrine of equivalents.

Prosecution history estoppel

The Treaty further states that in determining the extent of protection, due account must be taken of any statement limiting the scope of the claims made by the applicant or the owner of the patent during procedures concerning the grant or the validity of the patent, respectively. The question thus arises as to what extent this impacts the scope of protection of a patent.

Patent practitioners generally agree that determining the scope of protection of a patent is one of the most challenging topics in patent law and may often result in points of contention. In determining the protection scope, a patent owner may adopt an ambiguous attitude. For example, the patent owner may:

  • insist on a rather limited and narrow reading of the claims during patent grant or invalidity proceedings to avoid one or more novelty and/or inventive step objections and thereby increase the likelihood of a patent right being granted or maintained; and
  • use, in subsequent infringement proceedings, a broader claim interpretation to bring certain allegedly infringing acts within the scope of protection of the patent.

This principle is known as the "Angora cat paradox".

To prevent the patentee from taking such a position, prosecution history estoppel (PHE) was established in the United States. PHE may limit the range of infringement available under the doctrine of equivalents. Moreover, according to established US patent practice, PHE prevents a patentee from using the doctrine of equivalents to recapture subject matter that was initially surrendered during patent grant or invalidity proceedings from the scope of a claim.

Specifically, PHE may arise from a variety of acts taken by the patentee during patent prosecution. For example, it is well settled that claim amendments made in response to prior art rejections can result in PHE. In addition, PHE may also be created by arguments and representations made by the patentee to (foreign) patent offices to obtain allowance of a patent right, even without a claim amendment.

There is no direct legal basis in the EPC nor in the Protocol to oblige the national courts of the contracting states to apply PHE. Additionally, PHE is not provided under the respective national patent laws of most contracting states. However, to safeguard the legal certainty of third parties, PHE is often provided by national jurisprudence. Indeed, to determine patent infringement, the vast majority of the national courts of the EPC contracting states may take into account arguments raised by the patentee during patent grant or invalidity proceedings.

Therefore, the use of PHE may play an important role when applying the doctrine of equivalents for determining the scope of protection of a European patent and subsequently deciding on patent infringement. A patentee that has limited the scope of protection conferred by claims of a granted patent by filing claims that are more limited in scope during prosecution of the patent application should have no right during subsequent infringement proceedings to obtain protection for subject matter which it is deemed to have abandoned earlier due to the limitation of scope of the claims.

For further information on this topic please contact Olivier Van der Poorten at GEVERS by telephone (+32 2 715 3711) or email ([email protected]). The GEVERS website can be accessed at