The purpose of this bachelor thesis is to find how and if tags are used in Swedish library catalogues. Two different library catalogues from two different vendors were studied. One is from the Swedish company Axiell and the other one is from Open Library Solution. The tags were gathered from twenty books that were tagged in both catalogues. The books were a mix of both adults and children’s literature, and these were also from different genres.The following questions are asked: What features are user tags in comparison with classical indexing? What types of books are the most tagged? The theoretical framework of the thesis is based on F.W Lancaster´s theory about indexing.The result of this bachelor thesis is that tags are mostly used to identify the content of the books and the most popular type of tags is those who describe the content of the book. They are also used to identify what the books are or are used for, as a prizewinning novel or in an activity at the library. The group of users who are using tagging the most seems to be fantasy readers and possibly the library staff. The bachelor thesis ends in a discussion if libraries can learn from them what makes tagging interesting for library patrons.