This manual was developed for Compliance Safety and Health Officers (CSHO) of the Occupational Safety and Health Administration (OSHA) to help them carry out their responsibilities when investigating workplace accidents. The content is presented in four sections. The first overviews the investigative roles of CSHO officers, including preinvestigation, onsite, and courtroom activities. Section 2 on investigative techniques discusses site documentation, interviewing, and accident scene examination. The next section covers causal factors analysis and reporting, while the last one summarizes the manual. (EM)