1. A system for selecting a behavior to be executed by an improvisational character, the system comprising: a) a memory means for storing a set of possible behaviors for the character and for storing state data representative of a current state of the character, the current state comprising a current mood having a mood dimension, the state data including a mood value on the mood dimension, the memory means also storing for each of the possible behaviors a respective mood rating of the possible behavior on the mood dimension; and b) a processor means in communication with the memory means for selecting the behavior to be executed from the set of possible behaviors, the processor means including: i) an identification means for comparing the mood rating of each of the possible behaviors to the mood value to identify from the set of possible behaviors a subset of feasible behaviors for the character in the current state and in the current mood, ii) an evaluation means for determining for each of the feasible behaviors a respective desirability rating of the feasible behavior in the current state, and iii) a selection means for selecting the behavior to be executed from the subset of feasible behaviors, wherein the behavior to be executed is selected in dependence upon its desirability rating.