A review. The midbrain dopaminergic system is traditionally considered as a 'common neural currency' for rewards of most kinds. There are several competing hypotheses of its precise contribution in behavior: 1) dopamine mediates the pleasure of rewards; 2) dopamine signals a reward prediction error and, thus, is involved in associative learning; 3) dopamine motivates the pursuit of rewards. However, some investigations have questioned the role of the midbrain dopamine in all these processes. Considerable evidence has illustrated that dopamine system is crucially involved in learning and prediction processes, in estimation of the results of activity, in novel stimulus salience attributions, in decision-making processes and, the most important, in estimation of uncertainty. Such mysterious modulation provides our spontaneity and protects against high reactivity.