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 Michigan, evidence is crucial in both civil and criminal proceedings and must adhere to the Michigan Rules of Evidence. These rules determine what evidence is admissible in court. For evidence to be admitted, it must be relevant, meaning it must have any tendency to make a fact more or less probable than it would be without the evidence and that the fact is of consequence in determining the action. Physical evidence, like written agreements, and digital evidence, such as emails, must be authenticated to be admissible. Testimony from witnesses must be based on personal knowledge. Expert witness testimony is subject to a reliability standard; the expert's knowledge, skill, experience, training, or education must be established, and their testimony must be based on sufficient facts or data and be the product of reliable principles and methods that have been applied reliably to the facts of the case. The judge acts as the gatekeeper in determining the admissibility of evidence, including the reliability of expert testimony.