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 New Jersey, an offer of proof is a procedural mechanism 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. 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 preserve the excluded evidence for appellate review, providing the appellate court with a context to assess whether the trial court's exclusion of the evidence was erroneous and whether it may have affected the outcome of the case. On the other hand, a formal bill of exception, which is less commonly used in modern practice due to changes in rules of appellate procedure, serves a similar purpose. It allows a party to detail evidence that was not put into the trial record because no offer of proof was made. This procedure ensures that the appellate court is aware of the excluded evidence when reviewing the trial court's decisions. Both offers of proof and bills of exception are important for preserving issues for appeal, ensuring that a party's right to a fair trial is maintained even when evidence is excluded at the trial level.