The purpose of this research is to study the phenomenon of the “known-item search,” to investigate and map out its parameters. The research reported on here is the result of pretesting a survey that will be administered to public and academic library users looking for a particular book, asking them about the extent to which they would accept the substitute of a related item for the one they are looking for. The research is being framed in terms of the 1998 document model, Functional Requirements for Bibliographic Records (FRBR), in which different levels, or aspects, of content have been identified. FRBR is being incorporated into international library cataloging standards, however, research is only now beginning to be conducted to test the applicability of the model to people who are actually searching for documents. The study has two purposes: first, to improve information systems, particularly online catalogs, using specific knowledge of the range of acceptable items that may be the object of a search, and second, to determine the extent to which the FRBR model is useful in describing entities of interest to library users.