The online manifestation of medical and health services can be considered under two broad headings: (I) databases from which information can be downloaded by users and (2) transactional services through which users interrogate medical and health professionals about personal health issues. Early transactional services operated via telephone links. These are now being enhanced or superseded by new electronic communications formats operating via the Internet. In due course, further technological developments, as outlined later in this book, will involve interactive digital television as a primary information source and communications medium for health applications. The rapid growth of computer-mediated communication systems, including the Internet and World Wide Web and interactive digital television, has opened up possibilities for the public and, more especially, patients to become better informed about health issues and to take more responsibility for health care decisions. Many online information services were originally developed primarily for medical and health professionals, although attract as many if not more lay users (Lindberg, 2002).