A summons is typically issued alongside a complaint when a lawsuit is filed, and it formally notifies the defendant that they have been sued and must respond within a specific deadline, often within a few weeks depending on the jurisdiction. Being served with a summons makes someone a party to the case, meaning they have the right (and generally the obligation) to respond, or risk a default judgment being entered against them.

Summonses can also appear outside civil lawsuits — for example, a criminal summons directing someone to appear in court to answer charges, rather than being arrested. In both contexts, the summons establishes that the recipient is now formally part of a legal proceeding.

A subpoena is a legal order requiring someone to do something specific related to a case — commonly to testify at a deposition or trial (a subpoena ad testificandum), or to produce documents or records (a subpoena duces tecum). Unlike a summons, a subpoena can be directed at someone who is not a party to the lawsuit at all, such as a witness, an employer with relevant records, or a third-party business.

Subpoenas are typically issued by an attorney or the court as part of the discovery process or trial preparation, and they carry legal force — ignoring a valid subpoena without a proper legal objection can result in being held in contempt of court.

A summons makes someone a party to a lawsuit with obligations to formally respond to the claims against them; a subpoena obligates someone — whether or not they are a party — to provide testimony or documents relevant to someone else's case. Someone who receives a subpoena is not being sued and has not been accused of wrongdoing merely by being subpoenaed.

The deadlines and required responses also differ: a summons generally requires filing a formal answer or response with the court, while a subpoena generally requires appearing at a specified time and place, or producing specified documents, sometimes with the option to object or seek to limit the subpoena's scope through the court.

If served with a summons, responding by the stated deadline is critical — missing it can result in a default judgment without ever having the chance to present a defense. Consulting an attorney promptly after being served helps ensure the response is properly filed and any defenses are preserved.

If served with a subpoena, reviewing what is actually being requested — and whether there are valid grounds to object, such as the request being overly broad, privileged, or unduly burdensome — is an important step before simply complying or ignoring it. An attorney can help evaluate whether to comply, negotiate the scope, or formally challenge the subpoena in court.