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Federal Rules of Civil Procedure
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Federal Rule of Civil Procedure 45 governs subpoenas that may seek testimony or information from non-retained experts and other professionals. This article explains protections for unretained experts, fact versus expert testimony, substantial need and compensation, motions to quash or modify, and how Rule 45 interacts with Rule 26 disclosures and Rule 702 admissibility.
Federal Rule of Civil Procedure 45 governs subpoenas for testimony, documents, electronically stored information, tangible things, and inspections in federal civil litigation. When a subpoena targets a professional with specialized knowledge, a key question is whether it seeks firsthand evidence or expert opinion from someone who was not retained for the case.
Rule 45 protects certain unretained-expert opinions and study-derived information. In some circumstances, a court may still require compliance if the serving party shows substantial need that cannot otherwise be met without undue hardship and ensures reasonable compensation.
This guide explains how Rule 45 applies to unretained experts, how courts distinguish factual evidence from expert analysis, and how Rule 45 interacts with expert disclosure and admissibility requirements.
Rule 45 allows a subpoena to require testimony, production of documents or electronically stored information, production of tangible items, or an inspection. Although the subpoena issues from the court where the action is pending, Rule 45(c) limits where compliance may be required.
For trials, hearings, and depositions, Rule 45(c)(1)(A) permits a subpoena to command attendance within 100 miles of where the person resides, is employed, or regularly transacts business in person. Rule 45(c)(1)(B) provides limited within-state exceptions. A party or a party's officer may be commanded to attend within the state, while a nonparty may be commanded to attend a trial elsewhere within the state only if doing so would not cause substantial expense. For other discovery, production of documents, electronically stored information, or tangible things must be commanded at a place within 100 miles of where the person resides, is employed, or regularly transacts business in person. Inspection of premises must occur at the premises to be inspected.
Rule 45(d)(1) also requires the party or attorney responsible for issuing and serving a subpoena to take reasonable steps to avoid imposing undue burden or expense. The court for the district where compliance is required must enforce that duty and impose an appropriate sanction on a party or attorney who fails to comply. The sanction may include lost earnings and reasonable attorney's fees.
Federal Rule of Civil Procedure 45 governs subpoenas for testimony, documents, electronically stored information, tangible things, and inspections in federal civil litigation. When a subpoena targets a professional with specialized knowledge, a key question is whether it seeks firsthand evidence or expert opinion from someone who was not retained for the case.
Rule 45 protects certain unretained-expert opinions and study-derived information. In some circumstances, a court may still require compliance if the serving party shows substantial need that cannot otherwise be met without undue hardship and ensures reasonable compensation.
This guide explains how Rule 45 applies to unretained experts, how courts distinguish factual evidence from expert analysis, and how Rule 45 interacts with expert disclosure and admissibility requirements.
Rule 45 allows a subpoena to require testimony, production of documents or electronically stored information, production of tangible items, or an inspection. Although the subpoena issues from the court where the action is pending, Rule 45(c) limits where compliance may be required.
For trials, hearings, and depositions, Rule 45(c)(1)(A) permits a subpoena to command attendance within 100 miles of where the person resides, is employed, or regularly transacts business in person. Rule 45(c)(1)(B) provides limited within-state exceptions. A party or a party's officer may be commanded to attend within the state, while a nonparty may be commanded to attend a trial elsewhere within the state only if doing so would not cause substantial expense. For other discovery, production of documents, electronically stored information, or tangible things must be commanded at a place within 100 miles of where the person resides, is employed, or regularly transacts business in person. Inspection of premises must occur at the premises to be inspected.
Rule 45(d)(1) also requires the party or attorney responsible for issuing and serving a subpoena to take reasonable steps to avoid imposing undue burden or expense. The court for the district where compliance is required must enforce that duty and impose an appropriate sanction on a party or attorney who fails to comply. The sanction may include lost earnings and reasonable attorney's fees.
Rule 45 uses the term "unretained expert" while Rule 26 addresses expert witnesses according to different disclosure requirements. The distinction matters because Rule 26 and Rule 45 address different procedural questions.
Unless otherwise stipulated or ordered by the court, Rule 26(a)(2)(C) requires a summary disclosure for certain expert witnesses who are not required to provide a Rule 26(a)(2)(B) written report. Rule 45(d)(3)(B)(ii), by contrast, addresses subpoenas requiring disclosure of certain unretained-expert opinions or study-derived information.
On motion, a court may quash or modify a subpoena requiring disclosure of an unretained expert's opinion or information that does not describe specific occurrences in dispute and results from a study not requested by a party.
A professional's specialized knowledge alone does not automatically trigger Rule 45 protection. The analysis depends on what the subpoena seeks and how the requested information arose.
Rule 45 distinguishes mandatory grounds for quashing or modifying a subpoena from protections the court may apply in its discretion.
Under Rule 45(d)(3)(A), on a timely motion, the court for the district where compliance is required must quash or modify a subpoena that:
Fails to allow a reasonable time to comply.
Requires compliance beyond Rule 45(c)'s geographic limits.
Requires disclosure of privileged or otherwise protected matter when no exception or waiver applies.
Subjects a person to undue burden.
Rule 45(d)(3)(B)(ii) also permits a court to quash or modify a subpoena seeking certain unretained-expert opinions or study-derived information.
Under Rule 45(d)(3)(C), in the circumstances described in Rule 45(d)(3)(B), the court may instead order appearance or production under specified conditions if the serving party shows a substantial need for the testimony or material that cannot otherwise be met without undue hardship and ensures that the subpoenaed person will be reasonably compensated. If the subpoena commands attendance, Rule 45(b)(1) separately requires tendering the fees for one day's attendance and the mileage allowed by law when the subpoena is served, except when the subpoena issues on behalf of the United States or one of its officers or agencies. Federal statutory witness fees and allowances are generally governed by 28 U.S.C. § 1821.
The Advisory Committee Notes make clear that experts are not categorically exempt from giving evidence, although Rule 45 provides specific protection for qualifying unretained-expert material.
A witness's profession does not, by itself, determine whether requested testimony is factual or expert in nature. A treating physician, engineer, inspector, accountant, investigator, or other professional may possess firsthand factual knowledge and may also have opinions formed during ordinary professional involvement in the events at issue.
Testimony about firsthand observations may constitute fact testimony, while an opinion that depends on scientific, technical, or other specialized knowledge may constitute expert testimony even if the opinion was formed before the litigation. Under the Rule 45 Advisory Committee Notes, the difference between requiring testimony about a previously formed or expressed opinion and requiring the witness to form a new opinion is a factor informing the court's discretion. It is not, by itself, a categorical dividing line between fact and expert testimony.
A subpoena raises particular concerns when it would require the professional to:
Develop a new opinion for the litigation.
Apply specialized methodology to facts not previously analyzed.
Review new records or products and reach a litigation-specific conclusion.
Extend independent research to circumstances the professional never studied.
Perform new calculations, testing, comparisons, or professional analysis.
Calling requested testimony "factual" does not make it factual. Courts may examine the substance of what the witness is being asked to provide and whether answering would require specialized knowledge or expert analysis.
The Advisory Committee Notes to Rule 45 cite Kaufman v. Edelstein, 539 F.2d 811, 822 (2d Cir. 1976) and identify several considerations that may guide the court's discretion:
Whether the witness is sought for relevant factual knowledge rather than opinion testimony.
Whether the subpoena seeks an existing opinion or requires a new one.
Whether the witness possesses unique expertise.
Whether comparable willing experts are available.
Whether repeated testimony demands have become oppressive.
These considerations do not replace Rule 45 but may help courts evaluate subpoenas seeking an unretained expert's specialized knowledge.
Kaplan v. General Electric Company, No. 2:22-CV-05296 (BRM) (SDA) (D.N.J. Feb. 21, 2025) provides an example of how one federal court applied Rule 45 when distinguishing firsthand evidence from independent expert work.
The subpoena targeted engineer Stephen Olenick, who had conducted independent testing involving a Honeywell alarm unit for a nonparty in work unrelated to the litigation. He had not tested the General Electric or Interlogix systems at issue and had not been retained by either side.
The court concluded that the subpoena sought Olenick as an expert rather than as a fact witness and found that the defendants had not established substantial need. The relevant report was available, and other information could be obtained through less intrusive discovery. The subpoena was quashed.
Kaplan illustrates that courts may look beyond how testimony is labeled and consider what the witness is actually being asked to provide.
Rule 45, Rule 26, and Federal Rule of Evidence 702 address different questions.
Rule 45 governs whether testimony or material may be compelled by subpoena.
Rule 26(a)(2) governs expert disclosure obligations for witnesses a party may use at trial to present evidence under Federal Rules of Evidence 702, 703, or 705. Depending on the witness, disclosure may require a written report under Rule 26(a)(2)(B) or a summary disclosure under Rule 26(a)(2)(C).
Rule 702 governs admissibility. The witness must be qualified by knowledge, skill, experience, training, or education, and the proponent must demonstrate to the court that it is more likely than not that Rule 702(a) through (d) are satisfied.
Compliance with a subpoena does not make an expert opinion admissible, and Rule 26 disclosure does not resolve every Rule 45 issue involving a nonparty.
For more on Rule 26 classifications, see Retained vs. Non-Retained Experts: Understanding Their Roles in Legal Cases. The article Can a Non-Retained Expert Witness Be Compelled to Testify at Deposition? addresses the deposition-specific issue.
Before subpoenaing a professional, counsel should identify exactly what information is needed and distinguish existing facts or previously formed opinions from new expert analysis. Counsel should also consider whether comparable information is available from documents, parties, other witnesses, or a retained expert.
A subpoena recipient should consider what testimony or production is requested, where compliance is required, and whether burden, privilege, or other protections apply. The recipient should also assess whether compliance would involve existing information or require new professional work.
For a subpoena commanding document production or inspection, Rule 45(d)(2)(B) permits written objections before the earlier of the compliance date or 14 days after service.
A motion to quash or modify under Rule 45(d)(3) generally goes to the court for the district where compliance is required. Under Rule 45(f), that court may transfer the motion to the issuing court if the subpoenaed person consents or the court finds exceptional circumstances.
Can a non-retained expert be subpoenaed in federal court?
Yes. Expert status does not create a blanket exemption from a federal subpoena. Rule 45 may still protect an unretained expert when the subpoena seeks an opinion or study-derived information covered by Rule 45(d)(3)(B)(ii). Other Rule 45 protections may also apply.
Can a subpoena force an unretained expert to develop a new opinion?
Rule 45 gives courts discretion to protect certain unretained-expert opinions and study-derived information, and the Advisory Committee Notes distinguish existing opinions from demands that require a new one. The result depends on the subpoena, requested information, and applicable precedent.
Is a treating physician automatically protected as an unretained expert?
No. A treating physician may possess firsthand factual knowledge and professional opinions arising from treatment. Rule 45 protection depends on what the subpoena asks the physician to disclose or do, rather than simply on the witness's professional title.
What happens if protected expert information is genuinely necessary?
Under Rule 45(d)(3)(C), the court may order compliance under specified conditions when the serving party shows substantial need for the testimony or material that cannot otherwise be met without undue hardship and ensures reasonable compensation.
Does Rule 45 determine whether expert testimony is admissible at trial?
No. Rule 45 governs compulsory process. Rule 26 expert disclosure requirements and Rule 702 admissibility requirements remain separate issues.
Rule 45 uses the term "unretained expert" while Rule 26 addresses expert witnesses according to different disclosure requirements. The distinction matters because Rule 26 and Rule 45 address different procedural questions.
Unless otherwise stipulated or ordered by the court, Rule 26(a)(2)(C) requires a summary disclosure for certain expert witnesses who are not required to provide a Rule 26(a)(2)(B) written report. Rule 45(d)(3)(B)(ii), by contrast, addresses subpoenas requiring disclosure of certain unretained-expert opinions or study-derived information.
On motion, a court may quash or modify a subpoena requiring disclosure of an unretained expert's opinion or information that does not describe specific occurrences in dispute and results from a study not requested by a party.
A professional's specialized knowledge alone does not automatically trigger Rule 45 protection. The analysis depends on what the subpoena seeks and how the requested information arose.
Rule 45 distinguishes mandatory grounds for quashing or modifying a subpoena from protections the court may apply in its discretion.
Under Rule 45(d)(3)(A), on a timely motion, the court for the district where compliance is required must quash or modify a subpoena that:
Fails to allow a reasonable time to comply.
Requires compliance beyond Rule 45(c)'s geographic limits.
Requires disclosure of privileged or otherwise protected matter when no exception or waiver applies.
Subjects a person to undue burden.
Rule 45(d)(3)(B)(ii) also permits a court to quash or modify a subpoena seeking certain unretained-expert opinions or study-derived information.
Under Rule 45(d)(3)(C), in the circumstances described in Rule 45(d)(3)(B), the court may instead order appearance or production under specified conditions if the serving party shows a substantial need for the testimony or material that cannot otherwise be met without undue hardship and ensures that the subpoenaed person will be reasonably compensated. If the subpoena commands attendance, Rule 45(b)(1) separately requires tendering the fees for one day's attendance and the mileage allowed by law when the subpoena is served, except when the subpoena issues on behalf of the United States or one of its officers or agencies. Federal statutory witness fees and allowances are generally governed by 28 U.S.C. § 1821.
The Advisory Committee Notes make clear that experts are not categorically exempt from giving evidence, although Rule 45 provides specific protection for qualifying unretained-expert material.
A witness's profession does not, by itself, determine whether requested testimony is factual or expert in nature. A treating physician, engineer, inspector, accountant, investigator, or other professional may possess firsthand factual knowledge and may also have opinions formed during ordinary professional involvement in the events at issue.
Testimony about firsthand observations may constitute fact testimony, while an opinion that depends on scientific, technical, or other specialized knowledge may constitute expert testimony even if the opinion was formed before the litigation. Under the Rule 45 Advisory Committee Notes, the difference between requiring testimony about a previously formed or expressed opinion and requiring the witness to form a new opinion is a factor informing the court's discretion. It is not, by itself, a categorical dividing line between fact and expert testimony.
A subpoena raises particular concerns when it would require the professional to:
Develop a new opinion for the litigation.
Apply specialized methodology to facts not previously analyzed.
Review new records or products and reach a litigation-specific conclusion.
Extend independent research to circumstances the professional never studied.
Perform new calculations, testing, comparisons, or professional analysis.
Calling requested testimony "factual" does not make it factual. Courts may examine the substance of what the witness is being asked to provide and whether answering would require specialized knowledge or expert analysis.
The Advisory Committee Notes to Rule 45 cite Kaufman v. Edelstein, 539 F.2d 811, 822 (2d Cir. 1976) and identify several considerations that may guide the court's discretion:
Whether the witness is sought for relevant factual knowledge rather than opinion testimony.
Whether the subpoena seeks an existing opinion or requires a new one.
Whether the witness possesses unique expertise.
Whether comparable willing experts are available.
Whether repeated testimony demands have become oppressive.
These considerations do not replace Rule 45 but may help courts evaluate subpoenas seeking an unretained expert's specialized knowledge.
Kaplan v. General Electric Company, No. 2:22-CV-05296 (BRM) (SDA) (D.N.J. Feb. 21, 2025) provides an example of how one federal court applied Rule 45 when distinguishing firsthand evidence from independent expert work.
The subpoena targeted engineer Stephen Olenick, who had conducted independent testing involving a Honeywell alarm unit for a nonparty in work unrelated to the litigation. He had not tested the General Electric or Interlogix systems at issue and had not been retained by either side.
The court concluded that the subpoena sought Olenick as an expert rather than as a fact witness and found that the defendants had not established substantial need. The relevant report was available, and other information could be obtained through less intrusive discovery. The subpoena was quashed.
Kaplan illustrates that courts may look beyond how testimony is labeled and consider what the witness is actually being asked to provide.
Rule 45, Rule 26, and Federal Rule of Evidence 702 address different questions.
Rule 45 governs whether testimony or material may be compelled by subpoena.
Rule 26(a)(2) governs expert disclosure obligations for witnesses a party may use at trial to present evidence under Federal Rules of Evidence 702, 703, or 705. Depending on the witness, disclosure may require a written report under Rule 26(a)(2)(B) or a summary disclosure under Rule 26(a)(2)(C).
Rule 702 governs admissibility. The witness must be qualified by knowledge, skill, experience, training, or education, and the proponent must demonstrate to the court that it is more likely than not that Rule 702(a) through (d) are satisfied.
Compliance with a subpoena does not make an expert opinion admissible, and Rule 26 disclosure does not resolve every Rule 45 issue involving a nonparty.
For more on Rule 26 classifications, see Retained vs. Non-Retained Experts: Understanding Their Roles in Legal Cases. The article Can a Non-Retained Expert Witness Be Compelled to Testify at Deposition? addresses the deposition-specific issue.
Before subpoenaing a professional, counsel should identify exactly what information is needed and distinguish existing facts or previously formed opinions from new expert analysis. Counsel should also consider whether comparable information is available from documents, parties, other witnesses, or a retained expert.
A subpoena recipient should consider what testimony or production is requested, where compliance is required, and whether burden, privilege, or other protections apply. The recipient should also assess whether compliance would involve existing information or require new professional work.
For a subpoena commanding document production or inspection, Rule 45(d)(2)(B) permits written objections before the earlier of the compliance date or 14 days after service.
A motion to quash or modify under Rule 45(d)(3) generally goes to the court for the district where compliance is required. Under Rule 45(f), that court may transfer the motion to the issuing court if the subpoenaed person consents or the court finds exceptional circumstances.
Can a non-retained expert be subpoenaed in federal court?
Yes. Expert status does not create a blanket exemption from a federal subpoena. Rule 45 may still protect an unretained expert when the subpoena seeks an opinion or study-derived information covered by Rule 45(d)(3)(B)(ii). Other Rule 45 protections may also apply.
Can a subpoena force an unretained expert to develop a new opinion?
Rule 45 gives courts discretion to protect certain unretained-expert opinions and study-derived information, and the Advisory Committee Notes distinguish existing opinions from demands that require a new one. The result depends on the subpoena, requested information, and applicable precedent.
Is a treating physician automatically protected as an unretained expert?
No. A treating physician may possess firsthand factual knowledge and professional opinions arising from treatment. Rule 45 protection depends on what the subpoena asks the physician to disclose or do, rather than simply on the witness's professional title.
What happens if protected expert information is genuinely necessary?
Under Rule 45(d)(3)(C), the court may order compliance under specified conditions when the serving party shows substantial need for the testimony or material that cannot otherwise be met without undue hardship and ensures reasonable compensation.
Does Rule 45 determine whether expert testimony is admissible at trial?
No. Rule 45 governs compulsory process. Rule 26 expert disclosure requirements and Rule 702 admissibility requirements remain separate issues.
Federal Rules of Civil Procedure
Federal Rules of Civil Procedure