In Illinois, the decision to whether to admit expert testimony falls within the sound discretion of the trial court. A person will be allowed to testify as an expert witness if:

  1. His or her experience and qualifications afford him or her knowledge that is not common to laypersons, and
  2. his or her testimony will aid the trier of fact in reaching its conclusions.

There is no predetermined formula for how an expert acquires specialized knowledge or experience, and the expert can gain such through practical experience, scientific study, education, training, or research. Formal academic training or specific degrees are not required to qualify a person as an expert; practical experience in a field may serve just as well as to qualify him or her. An expert need only have knowledge and experience beyond that of an average citizen. The burden of establishing the qualifications of an expert witness is on the proponent of his or her testimony.1

In Thompson v. Gordon,2 the Illinois Supreme Court addressed the issue whether a professional engineer must be licensed in the State of Illinois pursuant to the Professional Engineering Practice Act of 1989 (“the Engineering Act”)3 in order to testify as a retained expert witness in an Illinois civil action.4 The trial court had barred a professional engineer from offering opinion testimony related to the design and construction of roadways solely because he was not licensed in Illinois as a professional engineer, even though he was licensed in the District of Columbia. The trial court concluded that participating as an expert witness in any pending litigation in Illinois would constitute the unlicensed practice of engineering under the Engineering Act.5

The Illinois Supreme Court in Thompson disagreed with the trial court, stating that while it may be a factor to consider, licensure with the State of Illinois pursuant to the Engineering Act was not a mandatory prerequisite to rendering an expert opinion in an Illinois civil action. Instead, as discussed above, the relevant considerations in determining whether a person may testify as an expert witness include:

  1. Knowledge, skill, experience, training, and education;
  2. whether that knowledge, skill, experience, training, and education afford the witness knowledge and experience beyond that of the average citizen; and
  3. whether the expert’s testimony will aid the trier of fact in reaching conclusions.

In reaching its decision, the supreme court also found significant that the Illinois legislature had specifically provided for expert witness standards in other statutes. The court stated that if the legislature wanted to condition expert testimony by an engineer on whether he or she held a state license, then it could have enacted a statute setting standards for such expert witness, as it had done in cases in which the standard of care applicable to a medical professional is at issue.6

The Illinois Supreme Court in Thompson, however, declined to consider whether the work of an engineer unlicensed in Illinois as an expert witness constitutes the unlicensed practice of engineering, reasoning the initial determination of that question was properly relegated to the Illinois Department of Financial and Professional Regulation. Among the many examples of the “practice of professional engineering” provided in the Engineering Act is forensic engineering.7 Although not defined in the Engineering Act, the American Society for Testing and Materials’ “Standard Guide to Forensic Engineering” (“SGFE”)8 defines the term forensic engineering as “the application of the art and science of engineering in matters which are, or may possibly relate to, the jurisprudence system, inclusive of alternative dispute resolution.”9 The SGFE lists the typical qualifications to testify as an expert in forensic engineering, including licensure; but, it expressly states that “[c]ourts may decide that individuals with qualifications other than those described herein can testify as experts in forensic engineering.”10 Thus, the SGFE—the industry standard—is consistent with the Thompson decision: Licensure is not a mandatory prerequisite to testifying as a forensic engineer and rendering an expert opinion in a civil case in Illinois.11

1 See, e.g., Snelson v. Kamm, 204 Ill.2d 1 787 N.E.2d 796 (2003); People v. Miller, 173 Ill.2d 167, 670 N.E.2d 721 (1996); People v. Jordan, 103 Ill.2d 192, 469 N.E.2d 569 (1989).
2 Thompson v. Gordon, 221 Ill.2d 414, 851 N.E.2d 1231 (2006).
3 225 ILCS 325/1 et.seq.
4 The Engineering Act defines a “professional engineer” as “a person licensed under the laws of the State of Illinois to practice professional engineering.” 225 ILCS 325/4(m). “Professional engineering” is defined in the Engineering Act as “the application of science to the design of engineering systems and facilities using the knowledge, skills, ability and professional judgment developed through professional engineering education, training and experience.” 225 ILCS 325/4(n).
5 See 225 ILCS 325/40.
6 735 ILCS 5/8-2501(c), which is part of the Illinois Code of Civil Procedure, allows the trial court to consider whether the proffered witness is licensed by any state or the District of Columbia in the same profession as the defendant in determining if he or she is qualified to testify as an expert and can testify on the issue of the appropriate standard of care.
7 225 ILCS 325/4(o).
8 ASTM E2713-11.
9 ASTM E2713-11, section 3.1.2.
10 ASTM E2713-11, section 4.2.
11 Prior to providing expert witness testimony in a jurisdiction other than Illinois, it is imperative that an engineer check with that jurisdiction to ensure he or she is in compliance with that jurisdiction’s laws.