As explained in the video below, interrogatories are a discovery device. During the discovery phase of a civil litigation the parties share and acquire evidence regarding the case. Interrogatories are written questions that parties use to acquire information and evidence from other parties in a civil litigation.
Interrogatories are written inquiries one party sends to the other party. Often, but not always, interrogatories are in the form of a question. Interrogatories might ask a party to describe an event that is relevant to the litigation or to name witnesses. The party receiving the interrogatory must usually respond in writing.
Because interrogatories are part of the discovery process, they are served before trial.
Let’s say one Penelope sues David for breaching a contract in which David promised to sell her his car. David asserts as an affirmative defense that in a conversation Penelope agreed to delay the sale for six months. In her interrogatories to David, Penelope could ask David when the conversation supposedly took place, where it took place, what was said, and whether anyone else was present for the conversation. These questions, and David’s responses, will enable the parties to better understand the issues before trial and to evaluate their claims and defenses based on the evidence.
Please keep in mind that rules for interrogatories can vary from state to state and also between federal court and state court. Interrogatories in the federal courts are governed by Rule 33.
The federal court for the Southern District of New York restricts the use of interrogatories. Initial interrogatories are limited to asking for the names of witnesses and regarding the computation of damages. See SDNY Local Rule 33.3