Altruism is a popular economic explanation for a wide range of pro-social decisions and actions. It has been applied frequently in several different streams of literature, and is a descriptively compelling model of behavior. This paper provides a theoretical framework for the existence of ordinal and cardinal altruistic value functions, as well as altruistic utility functions, based on an altruistic preference relation. Representation theorems are developed to specify relatively weak conditions under which altruistic value and utility functions can be shown (...) to exist. In addition, conditions that lead to additive forms of these functions are provided. (shrink)