The paper presents a conception of the AGENT-UM user modeling shell for students modeling purposes which will be integrated with the concept map based intelligent knowledge assessment system. The latter already has been developed and tested in several study courses at Riga Technical University. The AGENT-UM shell is an agents-based system, i.e. a multiagent system. It incorporates several useful features – open and editable user model, agent-based architecture, learning capabilities – that extend the functionality of existing user modelling shells. Key principles and requirements for the development of any modern user modelling shell are defined and explained. Software agents that will be used in the implementation of the AGENT-UM shell are described in details.