An offer of proof—also known as an informal bill of exception—is a procedure available during trial for the presentation of evidence the trial court has excluded. An offer of proof is made outside of the jury’s presence and often after the judge has sustained an objection to the admissibility of the evidence.

A bill of exception—also known as a formal bill of exception—is a procedure that allows a party to complain on appeal about evidence that would not otherwise appear in the trial record (because there was no offer of proof made at trial) by detailing the evidence (testimony, etc.) that would have been offered if the trial court had allowed it.

In Missouri, an offer of proof is a procedural mechanism used during a trial to create a record of evidence that the trial court has excluded. This is done outside the presence of the jury, typically after an objection to the evidence has been sustained by the judge. The purpose of an offer of proof is to ensure that the appellate court can review the decision to exclude the evidence, as it provides a clear statement of what the evidence would have shown had it been admitted. On the other hand, a formal bill of exception, also known as a bill of exceptions, is a written statement filed by an attorney that outlines the evidence or testimony that was not allowed by the court, which the attorney believes was a mistake. This document is used to preserve the issue for appeal when no offer of proof was made during the trial. Both procedures are important for preserving the record for potential appeals, ensuring that the appellate court can fully understand the context and impact of the trial court's evidentiary rulings.