Information which is organized in such a fashion that it deals with a single field or branch of knowledge, in contrast with problem-oriented information, which bears directly on a specific question asked or on a specific problem for which a solution is sought. A standard textbook or a descriptive book provide subject-oriented information, such as “all about physics” or “all about Hawaii”. A dictionary and a telephone book provide problem-oriented information, answers to the specific question “what does this word mean?” and “what is John Doe’s phone number?” A more complex example of problem-oriented information is found in a “how to” book. A chief distinction between the two classes of information source is that a problem-oriented source will draw from as many sources or fields of knowledge as necessary to deal with the problem, while a subject- oriented source deals, in the main, with a single discipline. Although there is a fundamental need for subject-oriented information, there is a strong movement toward providing information in the problem-oriented mode when such organization would be the most valuable for the user. A strong impetus has come with the computer, which brings a number of attributes: virtually unlimited memory, high-speed access to information, hypertext linkage, multimedia (sound and visual images, both still and in motion), and interactivity. One of the best examples of a problem-oriented information source is found in medicine in Problem Knowledge Couplers.