A catalog or catalogue, is a list of items that are organized in a systematic way and may include descriptive details. It can also refer to a pamphlet or book that contains such a list. It is a list or record of items. It is sometimes spelled catalogue. It commonly refers to a list of things being offered, such as items for sale or courses at a school.

It is the key to the holdings of any library which interprets the documents to the users. It informs the users what type and kind of documents are available and where they are located. The term catalogue originates from the two greek phrases Kata + Logos. Kata means according to and logos means order.