The intention for researching user studies has been in our minds since first decades of the last century. Over the last two decades has increased the interest for studying on user satisfaction. However, we have not emphasized that our ontological sense is to cover the users’ expectations. The purpose of this paper is establishing the importance of user satisfaction studies. It presents diverse themes: ontological sense of librarianship and information studies; background and definition of user satisfaction; methodological trends (theoretical models, methods, techniques, and measure instruments); and categories or variables which could determine user satisfaction.