CCP §98: A party may, in lieu of presenting direct testimony, offer the prepared testimony of relevant witnesses in the form of affidavits or declarations under penalty of perjury.

A party may, in lieu of presenting direct testimony, offer the prepared testimony of relevant witnesses in the form of affidavits or declarations under penalty of perjury. The prepared testimony may include, but need not be limited to, the opinions of expert witnesses, and testimony which authenticates documentary evidence. To the extent the contents of the prepared testimony would have been admissible were the witness to testify orally thereto, the prepared testimony shall be received as evidence in the case, provided that either of the following applies: (a) A copy has been served on the party against whom it is offered at least 30 days prior to the trial, together with a current address of the affiant that is within 150 miles of the place of trial, and the affiant is available for service of process at that place for a reasonable period of time, during the 20 days immediately prior to trial. (b) The statement is in the form of all or part of a deposition in the case, and the party against whom it is offered had an opportunity to participate in the deposition. The court shall determine whether the affidavit or declaration shall be read into the record in lieu of oral testimony or admitted as a documentary exhibit.