Quasi-criminal means a lawsuit or equity proceeding that has some, but not all, of the qualities of a criminal prosecution. It may appear in either a common law or a civil law jurisdiction. It refers to "a court's right to punish for actions or omissions as if they were criminal".^[1]

The origins of the phrase comes from the Latin language word, quasi, meaning somewhat, sort-of, alike or akin, to criminal law, as in quasi-contract.^[2] Quasi is used "to indicate that one subject resembles another, with which it is compared, in certain characteristics, but there are intrinsic and material differences between them".^[3]

During a civil or equity trial, a court may act as if it were a criminal case to punish a person for contempt of court.^[1] In some cases, a court may impose asset forfeiture or another penalty.^[4] For example, a court has the right to punish actions or omissions of a party in a child support case as if they were a criminal, penalizing the parent with a sentence of jail time.

Quasi-criminal proceedings include a wide variety of matters, including prosecution for a violation of law or ordinance, psychiatric matters, motor vehicle law, status offenses, family court actions, and equity proceedings such as a writ. What these various legal matters have in common are these factors:

• They may be instituted by a government agent on behalf of a private citizen, or
• They may be instituted by a private citizen on behalf of the government, ex rel.
• They implicate fundamental rights or constitutional rights, subjecting the law involved to strict scrutiny by the judiciary.^[1][5]
  • Because of that, they may be subject to the Miranda warning enunciated under the legal doctrine in Miranda v. Arizona^[5] or foreign counterparts.^[1]
  • They are subject to requirements for bail, if any.^[5][6]

Quasi-criminal actions include:

• A violation of law, offense, or ordinance, especially a motor vehicle law, parking ticket, or traffic ticket.^{[5][7][8][9][10]}
• Psychiatric matters, such as civil confinement, mental hygiene commitments, and similar proceedings.^[11]
• Regulatory offenses, such as health department violations, hunting or fishing without a license, and driving while intoxicated or ability impaired (D.W.I. or D.W.A.I.) when such is not a misdemeanor.^[8]
• Family court actions, including PINS (person in need of supervision) or truancy, juvenile delinquency, child support,^[1] paternity or filiation, child custody, and child visitation ("parenting time"). It may also include, in some states, a divorce action or family offense petition.
• Equity proceedings such as a writ, qui tam, contempt of court, bankruptcy, fraud, and the like.