The purpose of this report is to assist those involved in conducting recreational boating accident investigations, such as the U.S. Coast Guard, state marine police, and local law enforcement officers, in determining the cause and contributing factors of an accident. The information can be used as the basis for changes in education or enforcement practices, and/or initiating legislative or regulatory action to improve boating safety. The report brings together information about the techniques and methods of conducting an in-depth boating accident investigation, and serves as a training tool for organizations involved in accident investigation.