An expert witness is required in civil proceedings when a court, whether composed of a judge alone or a judge and jury, cannot determine an issue of fact without additional technical expertise. When an expert is engaged by a party, they owe a duty foremost to the Court to provide an impartial professional opinion regarding the subject for which they were engaged.

Rule 53.03 of the Rules of Civil Procedure governs the submission of expert evidence in Ontario.

Pursuant to sub-rule 53.03(2.1), an expert's report must contain:

1. The expert’s name, address and area of expertise.
2. The expert’s qualifications and employment and educational experiences in his or her area of expertise.
3. The instructions provided to the expert in relation to the proceeding.
4. The nature of the opinion being sought and each issue in the proceeding to which the opinion relates.
5. The expert’s opinion respecting each issue and, where there is a range of opinions given, a summary of the range and the reasons for the expert’s own opinion within that range.
6. The expert’s reasons for his or her opinion, including, (i) a description of the factual assumptions on which the opinion is based; (ii) a description of any research conducted by the expert that led him or her to form the opinion; and (iii) a list of every document, if any, relied on by the expert in forming the opinion.
7. A statement signed by the expert certifying that the expert is satisfied as to the authenticity of every authority or other document or record referred to in the report, other than, (i) a document or record consisting of evidence or potential evidence in the action that the expert analysed or interpreted in the report, if the document or record was provided to the expert by or on behalf of the party intending to call the expert as a witness; (ii) an authority or other document or record cited by the expert in the report only because it was referenced in a report prepared by another expert witness in the action and the expert is commenting on the reference; and (iii) an authority or other document or record referred to in the report the authenticity of which the expert doubts.
8. Details of the doubts the expert has respecting the authenticity of an authority, document or record described in subparagraph 6.1 iii, and of any doubts the expert may have respecting the authenticity of an authority, document or record described in subparagraph 6.1 i or ii.
9. An acknowledgement of expert’s duty (Form 53) signed by the expert.