California Evidence Code
(a) A person is qualified to testify as an expert if he has special knowledge, skill, experience, training, or education sufficient to qualify him as an expert on the subject to which his testimony relates. Against the objection of a party, such special knowledge, skill, experience, training, or education must be shown before the witness may testify as an expert.
(b) A witness' special knowledge, skill, experience, training, or education may be shown by any otherwise admissible evidence, including his own testimony.
(a) Subject to subdivision (b), a witness testifying as an expert may be cross-examined to the same extent as any other witness and, in addition, may be fully cross-examined as to (1) his or her qualifications, (2) the subject to which his or her expert testimony relates, and (3) the matter upon which his or her opinion is based and the reasons for his or her opinion.
(b) If a witness testifying as an expert testifies in the form of an opinion, he or she may not be cross-examined in regard to the content or tenor of any scientific, technical, or professional text, treatise, journal, or similar publication unless any of the following occurs:
(1) The witness referred to, considered, or relied upon such publication in arriving at or forming his or her opinion.
(2) The publication has been admitted in evidence.
(3) The publication has been established as a reliable authority by the testimony or admission of the witness or by other expert testimony or by judicial notice.
If admitted, relevant portions of the publication may be read into evidence but may not be received as exhibits.
(a) The fact of the appointment of an expert witness by the court may be revealed to the trier of fact.
(b) The compensation and expenses paid or to be paid to an expert witness by the party calling him is a proper subject of inquiry by any adverse party as relevant to the credibility of the witness and the weight of his testimony.
The court may, at any time before or during the trial of an action, limit the number of expert witnesses to be called by any party.