After reviewing the diagnostic criteria for mental retardation and the social development of mentally retarded persons, the manual outlines physical and behavioral symptoms of physical abuse, physical neglect, and sexual abuse. A description of applicable California Penal Code sections for charging crimes against the mentally retarded covers physical abuse or neglect and sexual abuse for both child and adult victims. The manual distinguishes between competency to give consent to sexual acts and competency to testify. Instruction in the initial investigation covers photographs, the medical examination, the victim interview, intelligence testing, and additional investigation. A discussion of preparation for court focuses on preparing the victim. A review of the preliminary hearing and trial includes a discussion of voir dire, which should give attention to potential jurors' credibility, their attitudes toward applicable law, and their attitudes about the retarded. The manual concludes with instruction in the presentation of evidence and argument. Appendixes present a sample of expert testimony at a preliminary hearing and questions to qualify a mentally retarded person as a witness. 15 footnotes and 11-item bibliography.