In days that seem very long ago, when the card catalog was the only way to search a library's collection, there was very little debate about the usability of the catalog. Librarians were most concerned about properly formatting catalog cards and, of course, ensuring that the cards were filed correctly. Today, the card catalog has been replaced in libraries by the Web Online Public Access Catalog (OPAC), which has more possibilities for customization and integration, and for outside access to the catalog. It has become important to design a Web catalog that not only follows the rules, but also is intuitive and easy to use for patrons who haven't yet learned the rules. In this column, the author describes several resources that are designed to help librarians evaluate the usability of these online catalogs.