A medical expert witness in California is a licensed physician or other medical professional who has expertise in a specific area of medicine and provides testimony as an expert witness in legal proceedings. The expert witness may be called upon to provide their professional opinion on a medical issue related to a case, such as a personal injury or medical malpractice suit. They may also review medical records, conduct research, and provide analysis to help support the case. Medical expert witnesses in California must be licensed to practice in the state, and typically have extensive experience and training in their area of specialty. They are often required to be impartial and provide unbiased testimony based on their medical expertise and the facts of the case.