Pretrial procedures are outlined, including the initial contact with the expert witness, examination of the client, and conference between counsel and expert witness. This initial conference is held to evaluate the use of the expert opinion in the trial or in settlement negotiations, to plan legal strategy, and to explore means of corroborating relevant and applicable pyschological theory. Next, the data-gathering and tactical planning for report, deposition, and trial is completed. For example, the psychiatrist can often supplement the counsel's familiarity with demographic theories of juror selection with a psychological evaluation of which prospective jurors can best 'listen' to the particular case. Another major task for the expert witness is the report to counsel, which should clarify the scope of the client's psychological behavior and its genesis and should contain carefully considered predictions of the client's responses to future situations and stresses. Finally, during the trial itself, the expert's qualifications are established and the data is presented. From this point, including the examination, cross-examination, and the redirect examination, all of the expert's testimony will be for the purpose of presenting an explanation of the opinion, requiring a full description of the theories, data-gathering techniques, and of the inferences drawn from the theory. In preparing expert witnesses for trial, counsel should make sure that witnesses have been fully instructed about the precise legal implications, of their task. In addition, the psychiatrist should be aware of the ethical implications of the role of the physician as witness in criminal proceedings. Examples of an affidavit and a petition for joint report of psychiatric testimony, and a list of 23 references are included.