Utility is taken to be an absolute, accurate measurement of how desirable something is; in particular, it differs from money in three key ways.

First, desire for it is linear (generally in economics and game theory a person with a lot of money receives less utility from an additional fixed amount of money than someone with very little money).

Second, when modeling a real situation, utility should include all external factors (the happiness received from doing a good deed, for instance).

Third, different people's utility is incomparable. It is meaningless to ask whether one person gets more utility from a situation than another person does. Utilities for a given person can be compared only to other utilities for that person.

A utility function is a function which specifies how much utility a player gets for a particular outcome. It maps the space of all possible strategy profiles to .