Will your case need an expert witness? Expert witnesses are used when you need to prove something which involves professional or technical knowledge, and expert witnesses (unlike fact witnesses) can offer an opinion to the court. For a basic description of expert witnesses, see this article from Slate. For family law cases, there can be many different types of expert witnesses needed. If custody is in dispute, an expert witness such as a doctor or mental health professional may be needed to evaluate and testify about either parent or the child. You may need an expert witness to look for and testify about information on your spouse's computer, or to track down hidden assets. If alimony is an issue, you may need an expert to evaluate and testify as to the spouse's ability to earn an income. You can also find expert witnesses for handwriting analysis, appraising assets and more. Last year, I testified as an expert witness in a case, it was an interesting experience to be on the other side of the witness stand!