Huge databases are being used in organizations to store data. These databases contain hidden patterns which can be discovered and used in the organization in different ways. In this book, a mechanism is proposed to discover hidden patterns in any large database in order to be used in a recommendation. This book, focused on circulation database of a library to discover and present related items. However, this technique could be used in other databases. The model is really simple and could be applied in any database to make a recommendation list and present it to users. In addition, a novel rule matrix is presented to store the found rules for future use. Both the list for recommendation and rule matrix are useful to construct a recommender system.