This report clarifies the sources of the tension between providers and payers with regard to what personal information should be shared for patients receiving mental health or substance abuse treatment. It also provides information to support a more consistent application of privacy-sensitive approaches to collecting personal health information in the future. It does not attempt to resolve the tension between providers and payers or specify what information should be shared. The study on which the report is based was conducted during the period September 2001–October 2002. It included a comprehensive literature review and discussions with 32 individuals in the mental health and substance abuse fields. Those interviewed included clinicians, patient advocates, experts on privacy issues, and representatives of provider associations, managed care trade associations, managed behavioral health organizations, and HMOs.