A subpoena is a formal legal document ordering someone to appear and testify, and it can also require the production of documents or other evidence. Subpoenas can be issued by attorneys as officers of the court or directly by the court itself, and are then served on the witness.

This tool applies to both parties in the lawsuit and to non-parties who may simply have relevant knowledge or documents, meaning bystanders or witnesses with no personal stake in the case can still be compelled to participate.

A witness who ignores a valid subpoena without a legitimate excuse risks being held in contempt of court, which can lead to fines or other penalties depending on the jurisdiction and the severity of the noncompliance.

Courts generally treat subpoenas seriously because the discovery and trial process depends on the ability to compel relevant testimony, so noncompliance is not typically treated as a minor issue.

Even in a civil case, a witness generally retains the constitutional privilege against self-incrimination if their testimony could expose them to criminal liability, allowing them to decline to answer specific questions on that basis.

Other recognized privileges, such as attorney-client privilege or certain protections for confidential communications, can also allow a witness to refuse to answer particular questions, though these privileges are typically narrow and must be properly asserted.

A witness who believes a subpoena is improper can generally file a motion to quash or modify it, arguing that it is unduly burdensome, seeks irrelevant information, or was not properly served under the applicable rules.

Courts weigh the need for the testimony or documents against the burden on the witness, and can narrow the scope of a subpoena rather than eliminating it entirely.