This paper presents considerations on altruism and prosocial behaviour formulated on the basis of some experiments with the ultimatum game. In the first part it will discuss relations between expected utility theories, the characteristics of homo oeconomicus and a modern understanding of altruism. It will focus in particular on conceptual differences, indicating that we can find more than one definition of altruism in modern literature. The second part of the text will provide an overview of selected behavioural theories of prosocial (...) behaviour. It will also present the manner in which needs, social determinants, norms, and individual psychological features affect the propensity to behave in a prosocial fashion. (shrink)