3.13 Opinion Testimony is a type of legal testimony where an expert witness provides his or her opinion on a particular issue relevant to the case. This type of testimony is usually based on facts that have been established in court and is used in civil or criminal trials. There are two main types of opinion testimony: lay opinion testimony and expert opinion testimony. Lay opinion testimony is given by witnesses who are not professional experts, but have some knowledge about the subject. Expert opinion testimony is given by witnesses who possess special knowledge, skill, or experience in the subject. Both types of opinion testimony can be used to help a jury or judge to reach a decision in a case.