Evidence is information that exists in physical or digital form—such as written agreements and e-mail communications—as well as testimony from witnesses who have personal knowledge of facts relevant to a dispute. Evidence generally must be relevant to be admitted in court and considered by the factfinder (judge or jury) in resolving a lawsuit. And some forms of evidence, such as expert witness testimony, must be shown to be sufficiently reliable (as determined by the judge) to be admitted in evidence.

In Maine, evidence is regulated by both state statutes and the Maine Rules of Evidence, which are closely modeled after the Federal Rules of Evidence. Evidence must be relevant to the issues in a legal dispute to be admissible in court, meaning it must have any tendency to make a fact more or less probable than it would be without the evidence and the fact must be of consequence in determining the action. Physical and digital evidence, such as written agreements and email communications, must be authenticated to be admitted. Testimony from witnesses, including expert witnesses, must be based on sufficient facts or data and be the product of reliable principles and methods that the witness has applied reliably to the facts of the case. The judge serves as the gatekeeper in determining the admissibility of evidence, including the reliability of expert testimony. Maine courts also adhere to the principle of excluding evidence if its probative value is substantially outweighed by the risk of unfair prejudice, confusion of the issues, or misleading the jury, among other considerations.