Pro per is an abbreviation of the Latin term in propria persona, which means “by one’s self.” In legal terms, it refers to someone who chooses to act as his or her own legal counsel in lawsuit, despite not being a lawyer. This term is synonymous with per se, which is usually used by federal courts. Pro per is commonly used by state courts, such as in California.

When a pro per litigant files legal papers, he or she must write “in pro per” on the bottom of the first page of the document, where, if there was legal counsel present, it would read “attorney for the plaintiff.” An old saying concerning pro per holds that "anyone who represents himself in court has a fool for a client and an ass for an attorney."

The Sixth and Fourteenth Amendments allow someone who is involved in a criminal prosecution to waive the right to counsel. However, once the defendant has elected to be pro per, he or she no longer has the right to be represented by an attorney. In civil law courts, there are no clear rules regarding the right to counsel. Courts allow for the submission of legal documents pro per, but they might not allow for corporations to appear in court without proper legal representation.

There are a number of reasons that a person may elect to be pro per instead of using proper legal counsel. One reason is the financial burden incurred with legal representation. A Strategic Lawsuit Against Public Participant (SLAPP) is specifically filed by a person or group of people to silence criticism from the defendant through the sheer financial costs of representing oneself in the lawsuit. Other reasons are the confidence a person has in being able to create a strong legal defense, the personal reasons for pursuing a case, and the inability find appropriate counsel.

One example of a pro per case is Van Orden vs. Perry. Thomas Van Orden, a destitute, successfully argued pro per his case for removing a public display of Ten Commandments, all the way to the Supreme Court. Van Orden was a lawyer, but with a suspended license. The Supreme Court decision was delivered on 27 June 2005, with a vote of five to four, stating that a public religious display did not violate the Constitution.