User models incorporate the knowledge about the user so as to increase, in a general sense, the effectiveness of man-machine interaction. Several applications or software agents can use such model-based knowledge to give better and personalized services to end-users. The personalization can be in the form of filtering, presentation, resolving ambiguity or incompleteness, and proactive notification.  In electronic commerce applications, the user interface plays a key role in achieving user acceptance. This is more so, in the case of business-to-consumer type e-commerce. Based on the user needs, we classify the shopping behavior of consumers into three categories, which are called comparative shopping, planned shopping and browsing-based shopping. We propose a user model to suit these buying behaviors. The user model described in this thesis can be helpful in the development of personalized services and for building user interface and software-agents that can assist consumers both reactively and pro-actively. The proposed user model is applicable in the context of virtual or electronic malls that deal with broad as well as specific types of products and services