Our work in this area focuses on three aspects: 1) developing the non-intrusive and real time sensing techniques (vision sensors and physiological sensors)for extracting various features typically characterizing the state of the user; 2) develop a probabilistic framework based on the Bayesian Networks to systematically integrate various sensory measurements to produce a composite index characterizing user's state; 3) determining the optimal assistance to provide to user in order to maintain user productivity and performance.