The difference between formal and informal discovery comes down to enforcement. Informal discovery is investigation you do on your own — interviewing willing witnesses, pulling public records, checking social media, ordering documents through Freedom of Information Act requests. Formal discovery uses court-backed tools authorized by procedural rules that legally compel the other side to answer questions, hand over documents, and sit for sworn testimony. Both happen during the pretrial phase of a civil lawsuit, and most cases use a combination of the two. The formal tools carry enforceable deadlines and real penalties for noncompliance, which is what gives them teeth.
The Core Difference
Informal discovery relies on cooperation and what’s already public. Nobody has to talk to you, and nobody has to give you anything they aren’t already required to make available. If a witness declines an interview or a company ignores your letter, you have no recourse.
Formal discovery relies on the court’s authority. In federal cases, it operates under Rules 26 through 37 of the Federal Rules of Civil Procedure.1Legal Information Institute. Federal Rules of Civil Procedure Rule 26 – Duty to Disclose; General Provisions Governing Discovery State courts have their own procedural rules, but most mirror the federal framework closely. When you serve a formal request, the other side has a fixed number of days to respond, and if they don’t, a judge can order them to comply and impose sanctions when they still refuse.
A note on scope before going further: this comparison is about civil litigation. Criminal cases operate under a separate framework, where the prosecution has a constitutional obligation to turn over evidence that could help the defendant — the Brady obligation — regardless of whether the defense asks for it.2U.S. Department of Justice. Justice Manual 9-5.000 – Issues Related to Discovery, Trials, and Other Proceedings Civil discovery, by contrast, depends almost entirely on the parties themselves requesting what they need.
What Informal Discovery Covers
Informal discovery often starts before a lawsuit is filed and continues throughout the case. Because none of it relies on the court’s authority, the quality of what you get depends entirely on who cooperates and what’s already publicly available.
Witnesses and Scene Investigation
Attorneys and investigators may reach out to people who saw what happened, asking them to describe their observations and sometimes signing written statements. Since these witnesses aren’t under subpoena, they can decline. A thorough investigation of the incident scene — documenting physical layouts, environmental conditions, or damage — often provides context no document can replace. The information gathered this way tends to be rougher than sworn testimony, but it shapes the formal requests that come later. You write much better interrogatories when you already have a general picture of what happened.
Public Records and Online Research
Government databases offer a surprising amount of useful material. Police and incident reports, property records, corporate filings, court records from other cases, and licensing records are all accessible without the other side’s cooperation. At the federal level, the Freedom of Information Act lets anyone request records held by federal agencies, though the process can take weeks or months and certain categories like law enforcement and national security records may be exempt.3FOIA.gov. Freedom of Information Act Most states have their own equivalents for state and local agencies.
Social media and other online footprints are another rich source. Publicly accessible posts, photos, reviews, and archived web pages can reveal admissions, contradictions, or timelines that strengthen your case. Confronting someone with their own social media post during a later deposition is far more effective than asking a vague open-ended question.
The Ethical Limit You Cannot Cross
Informal discovery has fewer procedural rules, but it isn’t unrestricted. The most important boundary: if you know the opposing party is represented by a lawyer, neither you nor anyone working on your behalf can contact that person directly about the case without their attorney’s consent.4American Bar Association. Model Rules of Professional Conduct Rule 4.2 – Communication with Person Represented by Counsel This rule applies to lawyers and their agents, including investigators, and violating it can result in disciplinary action and exclusion of any evidence obtained. Unrepresented witnesses are generally fair game, but misrepresenting your identity or purpose crosses a line in every jurisdiction.
What Formal Discovery Covers
Formal discovery uses structured tools authorized by court rules. Each one carries the court’s authority behind it, meaning the other side faces real consequences for ignoring or stonewalling your requests.
Interrogatories
Interrogatories are written questions the other side must answer in writing and under oath. They’re useful for nailing down basic facts: dates, identities, amounts, the basis for specific claims or defenses. Each side is limited to 25 interrogatories, including subparts, unless the court or a stipulation allows more. The responding party has 30 days to serve answers and objections.5Legal Information Institute. Federal Rules of Civil Procedure Rule 33 – Interrogatories to Parties
Requests for Production
A request for production compels the other side to turn over specific documents, electronically stored information, or tangible items for inspection and copying. This covers medical records, financial statements, emails, text messages, and internal company databases. When requesting electronic files, you can specify the format you want. If you don’t, the producing party must deliver them in the format they’re ordinarily maintained or in a reasonably usable form.6Legal Information Institute. Federal Rules of Civil Procedure Rule 34 – Producing Documents, Electronically Stored Information, and Tangible Things Electronically stored information has become the heaviest lift in modern discovery, and disputes over search terms, file formats, and data preservation are where many cases bog down.
Requests for Admission
Requests for admission ask the other side to confirm or deny specific facts or the genuineness of specific documents. Their purpose is to narrow the issues for trial by eliminating things that aren’t genuinely in dispute.7Legal Information Institute. Federal Rules of Civil Procedure Rule 36 – Requests for Admission If a party fails to respond within 30 days, the matters are automatically deemed admitted. That’s one of the most punishing defaults in all of discovery.
Depositions
A deposition is live, sworn testimony taken outside the courtroom. The witness answers questions from the opposing attorney while the testimony is recorded, typically by a stenographer, though audio and video recording are also permitted. Depositions are limited to one day of seven hours per witness, and each side gets a maximum of 10 depositions unless the court allows more.8Legal Information Institute. Federal Rules of Civil Procedure Rule 30 – Depositions by Oral Examination
Depositions are the most powerful formal discovery tool. Unlike interrogatories, which get filtered through the other attorney’s careful drafting, a deposition lets you see how a witness reacts in real time, follow up on evasive answers immediately, and pin down testimony that can be used to impeach the witness if their story changes at trial. They’re also the only formal tool that works on non-parties. You can depose anyone with relevant knowledge, not just the opposing side.
Physical and Mental Examinations
When a party’s physical or mental condition is central to the case, common in personal injury and disability disputes, the court can order that person to submit to an examination by a licensed professional chosen by the other side. This tool has a higher bar than the others. The requesting party must file a motion showing good cause and that the condition is genuinely in dispute, not just tangentially relevant.9Legal Information Institute. Federal Rules of Civil Procedure Rule 35 – Physical and Mental Examinations Courts don’t grant these routinely, and the examined party is entitled to a copy of the examiner’s report.
Subpoenas to Non-Parties
Formal discovery doesn’t only target your opponent. Under Rule 45, you can issue a subpoena to compel a non-party — a bank, an employer, a hospital, a former business partner — to produce documents or appear for testimony. This is how you get records that the opposing party doesn’t control or claims not to have. The procedures are stricter than party-to-party discovery: you must serve the subpoena on the non-party, give the opposing side notice, and comply with geographic and timing requirements. Non-parties can object or move to quash the subpoena if it’s unduly burdensome.
When to Use Which
Most cases start informal and escalate. Informal work builds the map: who was involved, what public records already exist, what the witnesses are likely to say, what documents you’ll need to demand. Formal discovery then goes after what informal methods can’t reach — the internal emails a company will never volunteer, the sworn testimony of a hostile witness, the financial records held only by the opposing party.
Two practical rules follow from this. First, don’t send formal requests you could answer yourself with a public records search or a quick review of the other side’s website. You’re burning your 25-interrogatory cap and your attorney’s hours on questions the world will already answer for free. Second, once you know a witness is likely to be uncooperative or evasive, stop trying to persuade them informally and reach for a deposition or subpoena. The court’s authority is what informal discovery lacks, and there’s no point in delaying its use once cooperation has failed.
What Happens When Someone Ignores You
This is where the difference matters most. If someone ignores your informal investigation, refuses an interview, declines to cooperate, you have no recourse. If someone ignores formal discovery, you can go to the judge.
The first step is a motion to compel under Rule 37, which asks the court to order the non-responsive party to comply.10Legal Information Institute. Federal Rules of Civil Procedure Rule 37 – Failure to Make Disclosures or to Cooperate in Discovery Most courts require you to certify that you tried to resolve the dispute informally before filing. If the motion succeeds and the other side still doesn’t comply, the court has a range of escalating sanctions:
- Deeming disputed facts established in your favor.
- Barring the non-compliant party from introducing certain evidence or pursuing certain defenses.
- Striking part or all of their pleadings from the record.
- Entering default judgment or dismissing the case entirely, the most severe outcome.
- Treating the defiance as contempt of court, which can carry fines and, in extreme cases, incarceration.
On top of any of these, the court must generally order the non-compliant party or their attorney to pay the other side’s reasonable expenses, including attorney’s fees, caused by the failure, unless the noncompliance was substantially justified.10Legal Information Institute. Federal Rules of Civil Procedure Rule 37 – Failure to Make Disclosures or to Cooperate in Discovery Judges don’t jump to the harshest sanctions immediately, but a pattern of obstruction gets you there faster than most litigants expect.
The Cost Difference
Informal discovery is relatively cheap. Your main expense is the time spent investigating, plus modest fees for public records requests or copies. Formal discovery is where litigation costs escalate quickly, and this surprises many people who assumed the expensive part of a lawsuit was the trial.
Depositions are the biggest single expense. Court reporter appearance fees and per-page transcript costs add up fast, particularly in cases with multiple witnesses. Video recording adds further cost. Electronically stored information is the other major expense driver. In document-intensive cases, reviewing, processing, and producing electronic files can dwarf every other litigation cost combined. Even interrogatories and document requests, while cheaper to send, require attorney time to draft, review responses, and negotiate objections.
All discovery, formal and informal, must seek information relevant to a claim or defense and proportional to the needs of the case. Rule 26(b)(1) lists six factors courts weigh: the importance of the issues at stake, the amount in controversy, each side’s relative access to the information, each side’s resources, how important the discovery is to resolving the case, and whether the burden or expense outweighs the likely benefit.1Legal Information Institute. Federal Rules of Civil Procedure Rule 26 – Duty to Disclose; General Provisions Governing Discovery A request that’s technically relevant but would cost $200,000 to fulfill in a case worth $50,000 isn’t getting past a judge. If your case involves less than six figures, talk with your attorney early about which formal tools are worth the expense and which informal methods can cover the same ground for less.