Union catalogs have been created in a range of media, including book format, microform, cards and more recently, networked electronic databases. Print union catalogs are typically arranged by title, author or subject (often employing a controlled vocabulary); electronic versions typically support keyword and Boolean queries.
Union catalogs exist in diverse formats, such as printed volumes, microfilms, cards, and most recently, online databases.  Print versions organize information by title, author, or subject, utilizing a structured vocabulary; electronic versions allow for searches using keywords and Boolean operators.