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 typically inadmissible in court under the Missouri Rules of Evidence, specifically Rule 802, which mirrors the general rule against hearsay found in 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, both Missouri law and federal law recognize numerous exceptions to this exclusionary rule. For instance, statements that are considered present sense impressions, excited utterances, statements of mental state, or made for medical diagnosis or treatment purposes, among others, may be admissible despite being hearsay. Additionally, statements that are not offered for the truth of the matter asserted, but for another purpose such as to show the effect on the listener or the declarant's state of mind, are not considered hearsay. The determination of whether a hearsay exception applies, or whether a statement is non-hearsay, is a nuanced decision that courts make based on the specific circumstances of each case.