Aimed at analyzing the psychological and social mechanisms that generate the so called information and formation needs, the categories "Activity" and "Communication" are analyzed as they are used in psychological sciences, as a conceptual system substratum related to needs, as well as the starting points to deduce the main determining of needs and existing needs. The treatment of this conceptual system in informational sciences is also presented. The main models, approaches and methods applied in researches for users and their needs are also exposed
