Although many children are excellent witnesses, some are too young to testify and others are not effective on the witness stand. Because evidence of child abuse is often difficult to obtain, expert testimony is important, especially in child sexual abuse cases. The use of expert testimony in criminal versus noncriminal proceedings is examined, principles of expert testimony are described, and various forms of expert testimony are identified. Types of information on which expert witnesses may rely to form opinions offered in court are noted, and expert testimony based on scientific principles is discussed. The important role of expert testimony in child physical abuse and neglect cases is considered, with emphasis on injury determination, battered child syndrome, shaken baby syndrome, Munchausen syndrome by proxy, and neglect. The importance of expert testimony in child sexual abuse cases is also addressed. The author points out certain types of expert testimony are not allowed by judges. 122 references and 3 notes