All patent re-examination requests are necessarily based upon new prior art not considered in an original examination. It is imperative to carefully develop a body of new art so the examiner has the strongest possible basis upon which new claims rejections can be formed. In this way, it can be impossible or at least very difficult for the patentee to argue his case in favor of patentability. If sufficiently strong prior art is introduced, the patent will fail in re-examination.

Foreign Patents
Prior art may come from many sources. Although a prior art reference is generally a US patent, it is not necessarily one. Foreign patents may also be considered as prior art. When examiners conduct an initial examination, 98% (guestimate) of the time the most important art relied upon is a U.S. patent and little consideration is given to foreign patents. However, foreign patents, even those published in a language other than English may sometimes be suitable prior art references for invalidating a U.S. patent. Therefore, an important first place to consider finding prior art sometimes lies in ‘offshore’ patent offices or non-U.S. patents.

Symposia presentations / Professional journals
As the idiom ‘publish or perish’ is alive and well in academia, another very good source of cutting edge and early scientific disclosure lies in science journals and professional symposia / technical conferences. Searches in these libraries may produce art not considered by patent examiners in a first conventional patent examination.

U.S. Patents
Despite the fact that most U.S. patents initial examination is based upon a body of prior art which largely includes U.S. Patents, the entire collection of U.S. patents is exceptionally large indeed. A considerable opportunity for missing important references is always present. Accordingly, careful searches of the U.S. patent library tend to produce important prior art not considered by the examiner.

Other Public Disclosure
While nearly all prior art is embodies as ‘printed matter’ it remains possible that prior art lies in other media forms. An ‘info-mercial’, or public speech, for example may include information which can be considered prior art. Thus, it is not necessary that a prior art reference by printed matter, but rather any public disclosure. Consider searches for prior art which extend past the traditional sources to find prior art not readily available to the examiner when his search was conducted.