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 Iowa, 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 whether that fact is of consequence in determining the action. Both physical and digital forms of evidence, such as written agreements and email communications, can be admitted as long as they meet the relevance criteria. Additionally, witness testimony is admissible if the witness has personal knowledge of the facts at issue. Expert witness testimony is subject to a reliability standard; the judge must find it sufficiently reliable based on the expert's qualifications, the methodology used, and the relevance of the testimony to the issues at hand. Iowa follows rules similar to the Federal Rules of Evidence, which provide a framework for determining the admissibility of evidence in court. The Iowa Rules of Evidence can be found in the Iowa Code, which attorneys reference to navigate the complexities of evidentiary standards in legal proceedings.