Book excerpt: Existing Online Public Access Catalogues (OPACs) demonstrate differences in the range and complexity of their functional features, terminology, and help facilities. While many libraries already have OPACs, there is a need to bring together, in the form of guidelines or recommendations, a corpus of good practice to assist libraries in designing or re-designing the displays for their OPACs, taking into consideration the needs of users. The audience for these guidelines is librarians charged with customizing OPAC software and vendors and producers of this software. The guidelines are mainly designed for general libraries with collections of resources in the humanities, the social sciences, and the pure and applied sciences. The guidelines are intended to apply to any type of catalogue, independently of the kind of interface and technology used.