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 South Dakota, evidence is regulated by both state statutes and rules of court, particularly the South Dakota Rules of Evidence. These rules dictate what evidence is admissible in court. Evidence 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 the fact must be of consequence in determining the action. Physical evidence, digital records, and witness testimony are all subject to these rules. Expert witness testimony is also governed by these rules, and the reliability of such testimony must be established before it can be admitted. The judge in a case acts as the gatekeeper for evidence, determining its admissibility based on relevance, reliability, and other factors such as whether the probative value is substantially outweighed by the risk of unfair prejudice, confusion of the issues, or misleading the jury. The South Dakota Rules of Evidence are consistent with the Federal Rules of Evidence, ensuring that evidence is presented in a manner that is fair to all parties and assists the factfinder in resolving the dispute.