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 Hawaii, an offer of proof is a procedural tool used during a trial when the court excludes evidence. This process allows the attorney to create a record of what the evidence would have shown, had it been admitted, by presenting it outside the jury's presence, typically after an objection has been sustained. The purpose of an offer of proof is to preserve the issue for appeal, by demonstrating to the appellate court the relevance and materiality of the excluded evidence. On the other hand, a bill of exceptions, or formal bill of exception, is a more antiquated method that was traditionally used to document objections to the court's rulings on the admissibility of evidence, which would not be apparent from the trial record alone. This would include a detailed account of the evidence that would have been presented. However, modern practice in many jurisdictions, including Hawaii, has largely replaced the formal bill of exceptions with a more streamlined process of making an offer of proof and including objections and offers in the trial transcript for the appellate record.