Healthcare technologies, include drugs, devices, biotechnologies and information systems. They are applied within the context of clinical doctrine and procedures, healthcare priorities, individual patient need, the skills and limitations of healthcare professionals and hospital administrative systems and financial resources. New tools, or emerging technologies, are developed within yet another context, that of basic and applied sciences, clinical trials, regulatory requirements, clinical acceptance and financial priorities. Overlaying all of these technical factors are the constraints and abstractions of ethics, law and religion and, of course, human hopes to prevent disease, minimize pain and disability and postpone death. Despite all this complexity new tools emerge, diffuse and often improve the quality and safety of patient care. Sometimes, however, patient outcomes are worse than they would have been had existing or alternative technologies been used to prevent, diagnose or treat disease. The process of collecting information on emerging healthcare technologies and predicting their impact is healthcare technology assessment and it is a primary function of the non-profit ECRI Institute. It is a dynamic interdisciplinary effort in which, because perceived evidence is often fragile and evanescent, we must revisit a given technology often until it is proven beyond a doubt or disappears. To do this we maintain extensive databases on both routinely used and emerging healthcare technologies. They are used by hospitals, ministries and departments of health, planners and health professionalsworldwide. This presentation provides case histories, lessons learned and cautions on the limitations of human judgement