Hearsay is a statement that (1) the person making it (the declarant) does not make while testifying at the current trial or hearing (in other words, the statement is made out of court); and (2) a party offers as evidence to prove the truth of the matter asserted in the statement.

Hearsay is generally not admissible as evidence—but there are many exceptions to hearsay, and statements that are non-hearsay. The law governing hearsay is usually located in the applicable state or federal rules of evidence, which are interpreted and applied by courts in court opinions or cases.

In Missouri, hearsay is generally inadmissible in court under the Missouri Rules of Evidence, specifically Rule 802, which mirrors the Federal Rules of Evidence. Hearsay is defined as an out-of-court statement made by someone other than the witness testifying at trial, which is offered to prove the truth of the matter asserted in the statement. However, there are numerous exceptions to this rule where hearsay can be admitted. These exceptions are outlined in Rules 803 and 804 of the Missouri Rules of Evidence and include, but are not limited to, statements made under the belief of impending death, statements against interest, certain public records, and statements made during the course of medical treatment. Additionally, some statements are defined as non-hearsay, such as a declarant-witness's prior statement or an opposing party's statement, as per Rule 801(d). The admissibility of hearsay in Missouri courts is ultimately determined by the judge, who will consider the rules and any relevant case law interpreting them.