There are various versions of the Doctrine of Equivalence. The two best known are:
1. The U.S. equitable doctrine developed to prevent someone from circumventing a patent by using substitutes for claim elements that have the same effect as the substituted element. If a substituted element performs the same function, in essentially the same way, with the same effect as the claimed element it may be regarded as an equivalent of the element and the claim may be infringed under the doctrine. Something similar to the doctrine of equivalents is, in some form, applied by most patent systems, but most broadly in the United States and in a more limited way in most other systems (where it will usually be referred to by other names). It is also limited by prosecution history estoppel (also known as file wrapper estoppel). Infringement that does not depend on the doctrine of equivalents is known as literal infringement. See §112 Equivalence, Reverse Doctrine of Equivalence.
2. The German version of the doctrine, which is analogous to the US doctrine, but differs from the US approach in the way that it compares the claimed invention and the accused embodiment. Under German law an accused embodiment is the equivalent of the patented invention if it fulfils three requirements:
- the embodiment solves the problem addressed by the invention with modified means which objectively have the same effect as the invention (Gleichwirkung);
- a person of skill in the art, would in light of the general technical knowledge extant as of the priority date, find the modified means as having the same or equivalent effect to the claimed means (Naheliegen); and
- the considerations applied by the skilled person in this assessment must sufficiently aligned with the technical objectives of the patent claim that the person skilled in the art considers the embodiment equivalent to the invention as defined by the claim (Gleichwertigkeit).
Thus under the German doctrine an accused embodiment may still infringe under the Doctrine of Equivalence, if it achieves the same objectives as the claimed invention. However, if the accused embodiment fails to achieve to any significant degree the benefits or objectives of the claimed invention, it will not infringe under the German doctrine. The German Doctrine of Equivalence is further limited by the Formstein Defence.
3. The line of English patent cases known as the Catnic/Improver cases is sometimes described as implementing the Doctrine of Equivalence, although this is not strictly correct.