Important points A testimony is a claim made by someone who has firsthand knowledge or expertise with a certain subject. Expert testimony is testimony provided by someone who is regarded an expert in a certain field due to education, training, certification, abilities, and/or experience. An expert may provide testimony in court cases as well as in other proceedings such as administrative hearings and civil trials. Expert witnesses can help judges and jurors understand subjects about which they might not be familiar. For example, an expert on toxic chemicals could testify about the effects that specific toxins have on the human body. Experts can also give opinions on matters relating to medical practices, diseases, symptoms, treatments, procedures, products, companies, organizations, etc. An expert's opinion is useful because it comes from someone who knows more about the subject at hand than the jury or judge. If you have questions about an incident or case in which you might want to offer an expert witness testimony, it is important to contact an attorney first before deciding what role you might want to play regarding this matter. If you decide to become an expert witness, there are several steps that need to be taken before you can be called to testify. First, you must disclose your intention to testify as an expert witness. Typically, you do this by filing a notice of intent with the court.