Librarians rely on the Institute for Scientific Information's journal impact factor as a tool for selecting periodicals, primarily in scientific disciplines. A current trend is to use this data as a means for evaluating the performance of departments, institutions, and even researchers in academic institutions--a process that is now being tied to tenure and promotion--despite the fact that such usage can be misleading and prejudicial. This paper will highlight the history of the development of impact factors, describe the limitations in their use, and provide a critique of the usage of impact factors in academic settings. (Contains 95 notes.)