A deposition in the law of the United States, or examination for discovery in the law of Canada, is the taking of sworn, out-of-court oral testimony of a witness that may be reduced to a written transcript for later use in court or for discovery purposes. Depositions are commonly used in litigation in the United States and Canada. They are almost always conducted outside court by the lawyers themselves, with no judge present to supervise the examination.

Depositions by written interrogatories first appeared around the mid-15th century as a procedure for discovery, factfinding, and evidence preservation in suits in equity in English courts. They differed radically from modern depositions in three ways: the party seeking a witness's testimony merely propounded written interrogatories which were read out loud by a master or court-appointed commissioner to the witness in a closed proceeding without parties or counsel present; the witness's first-person oral answers under oath were not recorded verbatim, but were summarized by the master, commissioner, or a clerk appointed by them into a third-person continuous narrative; and the resulting written product (also called a "deposition") was filed with the court under seal and its contents were not revealed or "published" to the parties until shortly before trial.

The modern deposition by oral examination began to develop in New York in the early 19th century when Chancellor James Kent of the New York Court of Chancery allowed masters to actually examine witnesses (that is, pursue lines of questions in real time based on the witness's preceding answers) rather than read static interrogatories (which tended to be broadly worded and resulted in very inefficient depositions). He also allowed parties and counsel to be present during depositions. This meant depositions were no longer secret and led to counsel insisting on taking over the examinations themselves. These developments gradually spread across the United States and Canada.

During the late 19th century, summary narratives by court-appointed examiners were replaced by verbatim transcripts by court reporters. Finally, the merger of common law and equity procedure led to the adoption of live testimony in open court as the default method of taking trial evidence in all trials (equity had used depositions by written interrogatories in lieu of live testimony), which reduced the deposition to its modern role in American civil procedure as a discovery and evidence preservation device.

In Canada, the process is nearly identical to that followed in the United States, but the proceeding is called an examination for discovery (French: interrogatoire préalable). Typically, the questions for the witness will be a mixture of direct questions and cross-examinations on prior statements. While most of the same objections to form are applicable as in the United States, the witness's lawyer may additionally take certain questions "under advisement" as a means of delaying answering the question, without making a formal objection.

The process is considered in Canada to be time-consuming and expensive when conducted without limits. As a result, Rule 31.05.1 of the Ontario Rules of Civil Procedure has, since January 1, 2010, limited examinations for discovery to seven hours per party except with consent of the other parties or the leave of the court. British Columbia implemented similar reforms on July 1, 2010, although the new Rule 7-2(2) can be read in two ways, it appears to be that each party can examine each other party for a maximum of seven hours unless the court orders otherwise. The alternative reading is that each party is only to be examined for a maximum of seven hours.

In mainland China, it is generally illegal to take depositions for use in foreign courts.

Deposition is the preferred term in U.S. federal courts and in the majority of U.S. states. In some unusual situations, depositions can be taken during or even after trial.