More accurately, a subpoena is the conditional threat of punishment made by a governmental authority. It is attached to a command, so that if the recipient does not do as commanded then he may be punished. Subpoenas are associated with common law legal systems.
There are two common types of subpoenas:
The term is from the Middle English suppena and the Latin phrase sub poena meaning "under penalty. The term may also be spelled "subpena.
The subpoena has its source in English common law and it is now used almost with universal application throughout the Anglo-American common law world. However, for Civil proceedings in England and Wales, the term has been replaced by witness summons, as part of reforms to replace Latin terms with English terms which are easier to understand.
Subpoenas are usually issued by the clerk of the court (see below) in the name of the judge presiding over the case. Additionally, court rules may permit lawyers to issue subpoenas themselves in their capacity as officers of the court. Typically subpoenas are issued "in blank" and it is the responsibility of the lawyer representing the plaintiff or defendant on whose behalf the testimony is to be given to serve the subpoena on the witness.
The subpoena will usually be on the letterhead of the court where the case is filed, naming the parties to the case, and being addressed by name to the person whose testimony is being sought. It will contain the language "You are hereby commanded to report in person to the clerk of this court" or similar, describing the specific location, scheduled date and time of the appearance. Some issuing jurisdictions include an admonishment advising the subject of the criminal penalty for failure to comply with a subpoena, and reminding him or her not to leave the court facilities until excused by a competent authority.
In non-criminal matters in U.S. Federal courts, the rules of procedure provide (in part):
Many state courts in the U.S. have adopted similar procedures.
Quashing the subpoena means the court declares it null and void, so one does not have to comply with it. For example, a court could quash a subpoena if the subject of the subpoena can show that compliance creates an undue burden.
Recently the Sixth U.S. Circuit Court of Appeals in Ohio upheld a ruling that placed a temporary injunction on e-mail searches with subpoenas, for violation of the Fourth Amendment. The 1986 federal Stored Communications Act (SCA) was being used to obtain e-mail from ISPs without warrants and without informing the targets of the investigation. The court held that subpoenas for emails need to include "prior notice and an opportunity to be heard" for the email account holder when the user has a reasonable expectation for privacy relating to the emails.
When considering whether to quash a federal subpoena, make sure the subpoena is not procedurally defective. Remember, the party who serves the subpoena must remember to (1) tender the required witness fees; (2) tender the estimated mileage; (3) properly state the civil action number; and (4) and state the method for recording deposition testimony.