At the beginning of a jury trial, both parties to the case may be required to submit a list of prospective witnesses. In a criminal case, it may be used to inform prospective jurors of who will likely testify, thus allowing prospective jurors to state if they know any of the witnesses and would therefore possibly be partial. However, disclosure of witness names can be subject to a protective order.
If either party desires the testimony of a given witness, that party must take the appropriate steps to obtain the witness’s presence at an appropriate time and in an appropriate fashion, and no party should assume a given witness will be produced by the other side simply because that witness’s name appears on the witness list, or has previously been identified as a potential or likely witness. Failure to include a witness on the required witness lists may result in that witness' testimony being prohibited at trial, or other sanctions. Court rules vary, so requirements in your jurisdiction should be consulted.
A supplemental witness list is obligated to be exchanged if any additions or changes are made to the originally supplied list.
The following is an example of a federal law governing witness lists:
"§ 13.22 Exchange of witness lists, statements, and exhibits.