Refers to a patent office proceeding to re-examine the grant of a patent, usually in light of prior art not before the patent office in the original examination. In the particular case of an ex parte re-examination, only the patent holder appears and makes arguments to the patent office, which obviously confers considerable advantages. All U.S. re-examinations used to be conducted on an ex parte basis, but recent legal changes provide for inter partes re-examinations where third parties, for example competitors, are allowed to be present and argue against the re-grant of the patent or for more limited claims. See Inter Partes Re-Examination.