Rule 701. Opinion Testimony by Lay Witnesses

If a witness is not testifying as an expert, testimony in the form of an opinion is limited to one that is:

(a) rationally based on the witness’s perception;

(b) helpful to clearly understanding the witness’s testimony or to determining a fact in issue; and

(c) not based on scientific, technical, or other specialized knowledge within the scope of Rule 702.

Rule 702. Testimony by Expert Witnesses

A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if the proponent demonstrates to the court that it is more likely than not that:

(a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;

(b) the testimony is based on sufficient facts or data;

(c) the testimony is the product of reliable principles and methods; and

(d) the expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.

Rule 703. Bases of an Expert’s Opinion Testimony

An expert may base an opinion on facts or data in the case that the expert has been made aware of or personally observed. If experts in the particular field would reasonably rely on those kinds of facts or data in forming an opinion on the subject, they need not be admissible for the opinion to be admitted. But if the facts or data would otherwise be inadmissible, the proponent of the opinion may disclose them to the jury only if their probative value in helping the jury evaluate the opinion substantially outweighs their prejudicial effect.

Rule 704. Opinion on an Ultimate Issue

(a) In General—Not Automatically Objectionable. An opinion is not objectionable just because it embraces an ultimate issue.

(b) Exception. In a criminal case, an expert witness must not state an opinion about whether the defendant did or did not have a mental state or condition that constitutes an element of the crime charged or of a defense. Those matters are for the trier of fact alone.

Rule 705. Disclosing the Facts or Data Underlying an Expert’s Opinion

Unless the court orders otherwise, an expert may state an opinion—and give the reasons for it—without first testifying to the underlying facts or data. But the expert may be required to disclose those facts or data on cross-examination.

Rule 706. Court-Appointed Expert Witnesses

(a) Appointment Process. On a party’s motion or on its own, the court may order the parties to show cause why expert witnesses should not be appointed and may ask the parties to submit nominations. The court may appoint any expert that the parties agree on and any of its own choosing. But the court may only appoint someone who consents to act.

(b) Expert’s Role. The court must inform the expert of the expert’s duties. The court may do so in writing and have a copy filed with the clerk or may do so orally at a conference in which the parties have an opportunity to participate. The expert:

(1) must advise the parties of any findings the expert makes;

(2) may be deposed by any party;

(3) may be called to testify by the court or any party; and

(4) may be cross-examined by any party, including the party that called the expert.

(c) Compensation. The expert is entitled to a reasonable compensation, as set by the court. The compensation is payable as follows:

(1) in a criminal case or in a civil case involving just compensation under the Fifth Amendment, from any funds that are provided by law; and

(2) in any other civil case, by the parties in the proportion and at the time that the court directs—and the compensation is then charged like other costs.

(d) Disclosing the Appointment to the Jury. The court may authorize disclosure to the jury that the court appointed the expert.

(e) Parties’ Choice of Their Own Experts. This rule does not limit a party in calling its own experts.