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 Maine, an offer of proof is a procedural tool used during a trial when the court excludes evidence. It allows the attorney to create a record of what the evidence would have shown, which is essential for appellate review. This is done outside the jury's presence, typically after an objection to the evidence has been sustained by the judge. The purpose is to demonstrate to an appellate court what the evidence would have been and how it could have affected the outcome of the trial. On the other hand, a formal bill of exception, which is less commonly used under modern rules of appellate procedure, is a written statement by the judge detailing the nature of the evidence that was excluded and the context in which the decision to exclude was made. This is used to preserve the issue for appeal when an offer of proof was not made during the trial. Both procedures are designed to ensure that the appellate court is aware of any potential errors regarding the admission or exclusion of evidence that could have influenced the trial's outcome.