The vital role of psychiatric evidence in court proceedings, including criminal, civil, and family court, has long been recognized by the legal profession and the judiciary. Best practice now dictates that lawyers apply their minds at an early stage of the proceedings to the issues in the cases to which medical evidence will be relevant. Lawyers are encouraged to make applications for leave to instruct an expert or experts at as early a stage as possible in case proceedings. The expert, once instructed, should express only opinions that he/she genuinely holds and that are not biased in favor of one particular party. The expert should not mislead by omissions. Experts should consider all the material facts in reaching their conclusions and must consider the material facts that could detract from their opinions. The expert's report should provide a clear opinion that is well reasoned based on expert knowledge, be objective and not omit factors that would detract from their opinion, and be properly researched. If an opinion is based on insufficient data because those data are not available, the expert should indicate this and state that any opinion is only provisional for this reason.