Selective Dissemination of Information (SDI) is one of the methods of providing current awareness services. Even though the term SDI was introduced by Hans Peter Luhn in 1958, to describe personalised current awareness service provided with the help of computers, librarians wee providing SDI service to their users from time immemorial. Unfortunately there are hardly any books published on this topic of great importance. Even though few doctorate degrees have been awarded in the subject of SDI in foreign countries; they have not been published and thus not easily available. A student or a researcher finds it very difficult to collect information on the topic of SDI. This book tries to fill up these lacunae. The book, no doubt, will be source book to students, researchers and information professionals throughout the world. It can act as the main source of information to the researchers who have taken up the task of evaluating the SDI services in any part of the world.