When a therapist becomes a courtroom witness, he/she often is in unfamiliar territory. Before appearing as a witness, a therapist must prepare by completely understanding the case and client, together with courtroom practices and procedures. This article reviews trial preparation and illustrates examination and cross-examination, opinion testimony and hypothetical questions. The rules of effective response to cross-examination are set forth to aid the therapist in providing meaningful and credible testimony under adverse and occasionally unpleasant conditions.