An interrogatory is a device typically used during the discovery phase of civil litigation. Interrogatories are written questions that are formally asked of the party. In federal court, they are governed by rule 33 of the Federal Rules of Civil Procedure. Unlike depositions, interrogatories may be served only on other parties to the litigation and are answered collectively by the legal team of the party rather than by the individual. The federal rules limit parties to no more than 25 written interrogatories.
Also under the federal rules, parties have 30 days to answer interrogatories and they must be answered fully, in writing and under oath. Objections can be made to interrogatories on grounds that they call for information that is protected by privilege, are irrelevant to the proceeding, call for attorney work product or similar objections.