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 Colorado, as in other jurisdictions, evidence must be relevant to be admissible in court. Relevance is determined by whether the evidence makes a fact more or less probable than it would be without the evidence and if that fact is of consequence in determining the action. Both physical and digital forms of evidence, such as written agreements and email communications, are subject to this standard. Additionally, witness testimony is considered evidence if the witness has personal knowledge of the facts relevant to the dispute. Expert witness testimony is subject to a reliability standard, which is assessed by the judge. The reliability of expert testimony is evaluated based on the methodology used, the expert's qualifications, and the applicability of the expert's methods to the facts of the case. This is in line with the Federal Rules of Evidence and the Colorado Rules of Evidence, which guide the admissibility of evidence in court proceedings. Certain types of evidence, such as hearsay, are generally not admissible unless they fall under an exception to the hearsay rule. The rules of evidence in Colorado are designed to ensure that the factfinder (judge or jury) considers only information that is pertinent and reliable in resolving a lawsuit.