This book reflects the enormous changes and advancements in the indexing and retrieval of online health information made possible by the Internet. The book summarizes technical state-of-the-art research results in health/medical information retrieval. Coupled with the growth of the World Wide Web, the topic of information retrieval has had a tremendous impact on consumer health information and genomics. When the First Edition was released in 1996, searching for health information on the Web was in its infancy. This book will chronicle the changes in the field that have occurred in the five years since that time. Just as the Internet is used by those all over the world, this book will reach across disciplines and address the needs of not only those who study, develop, evaluate, and purchase health information, but also computer and library/information scientists, information technology developers building databases, search engines, Web sites, and other systems for universities, companies, hospitals who enthusiastically read the First Edition. Heavily updated, the book provides an overview of the theory, practical applications, evaluation, and research directions of all aspects of medical information retrieval systems which will be presented in four sections covering basic principles, state of the art, research systems, and special topics. The table of contents includes terms, models, and resources; health information; system evaluation; content; indexing; retrieval; evaluation; statistical systems; linguistic systems; clinical narrative; multimedia; digital libraries; and the Internet. A well-developed course has been built around the First Edition at the Oregon Health Sciences University, where the author is a professor and and chief of the division of Medical Informatics and Outcomes Research, and the course is the basis for the newly added questions, discussions, and exercises that will follow each chapter. This book focuses on the indexing and retrieval of of online health information. It details technical state-of-the-art and research results in health/medical information retrieval. The increasing importance of health information retrieval makes the book an invaluable tool for those involved in this area, such as medical informaticians, computer scientists, library/information scientists, IT developers, and administrators from hospitals, companies, and universities who all enthusiastically read the First Edition. The book addresses the growth of the World Wide Web and its impact on consumer health information and genomics. When the First Edition was released 1996, the Web was in its infancy, but this is no longer the case. Thus, this edition will reflect the vast changes that have occurred in the field since 1996. Massively updated, this book is comprised of four sections covering basic principles, state of the art, research systems, and special topics. Drawing from his well-developed course at OHSU that was built around the First Edition, the author will add a question and discussion section. Covering theory, practical applications, evaluation, and research directions, the book's contents include terms, models, and resources; indexing; retrieval; statistical systems; lingusitic systems; clinical narrative; mulitmedia; digital libraries; and the Internet.