In a recent issue of the Atlantic Monthly, Cullen Murphy wrote that "It is always a little disconcerting when audacious scientific theories come a cropper." In this case, he was speaking of Stephen Hawking's now self-repudiated idea that information swallowed by cosmic black holes might be escaping into "baby universes." John Losee looks at the subject of rejected scientific theories through an analysis of case studies from more than two centuries of science. Losee excerpts the work of prominent scientists and philosophers of science accompanied by evaluative comments from the fields of science and philosophy. He sets these discussions within an analytical framework developed as answers to a sequence of questions about falsification, rejection, and theory replacement: When observational evidence conflicts with the assumptions of a theory, does this signify the death of the theory? If rival theories are available to account for an experience, how is the choice between them to be made? Are there generally accepted criteria against which competing theories may be assessed? When is the replacement of one theory by another justified? Each excerpt from each scientist or philosopher is of sufficient length to make clear the particular evaluative problem under consideration, and each discussion of scientific evaluative practice includes both what scientists and what philosophers have written on the topic. At a time when increasingly complex scientific questions must be considered and addressed in a variety of public forums, Theories on the Scrap Heap offers guidance for assessing the underlying assumptions and validity of scientific theory and for understanding how the scientific method works in theories formation and rejection.