There is not much time before the day in the future when the human-computer interaction will approach the communication between the humans to the extent that there will be minor intellectual differences. This contention is grounded on the huge amount of investigations and the encouraging results from the developments of various intelligent virtual agents. The intelligent virtual agents (IVA) are programming autonomous agents with graphically built human face (and often a body, too), existing in either 2D or 3D virtual environment. They have capabilities to interact intelligently with the surrounding environment including with other IVA as well as with the users of the corresponding application. In this monograph are discussed the main directions for intelligent virtual agent's modeling and realization. The objective of IVA's modeling is to use discovered patterns to help explain current behavior or to predict future outcome Great attention is paid to this direction, prove of which is the big amount of articles, program systems and tools for modeling. In this monograph the focus is placed on the consideration of IVA as a new computer's interface.