Many professional designations in the United States take the form of post-nominal letters. Certifications are usually awarded by professional societies or educational institutes. Obtaining a certificate is voluntary in some fields, but in others, certification from a government-accredited agency may be legally required to perform certain jobs or tasks.

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Organizations in the United States involved in setting standards for certification include the American National Standards Institute (ANSI) and the Institute for Credentialing Excellence (ICE). Many certification organizations are members of the Association of Test Publishers (ATP).

Additionally, many jurisdictions grant some or all judges the right to use postnominal letters, which they generally employ in lieu of "Esq." The most common is "J." (for "Judge" or ""Justice"), but more complex systems exist. For instance, in New Jersey, Judges of the New Jersey Superior Court are entitled to the postnomials "J.S.C.", except for the a Presiding Judges of the Family, Civil, Criminal, and General Equity Parts in a vicinage (entitled to the letters "P.J.F.P.", "P.J. Civ. P.", "P.J. Cr. P.", and "P.J. Ch. P."), a vicinage assignment judge (entitled to "A.J.S.C."), Appellate Division judges ("J.A.D.") and the Presiding Judge of the Appellate Division ("P.J.A.D."). Justices of the Supreme Court of New Jersey are entitled to the simple postnomial "J.", except for the Chief Justice, who uses "C.J."

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• List of post-nominal letters
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