when and why do young people tend to cooperate? ABstrActThe study explored young people's tendency for cooperation in different social conditions and explanations of behaviour given by them. Cooperation seems to be an important part of citizenship behaviour. Here, it is defined as a tendency to maximize common payoff. According to the Homo economicus theory, people are egoistic entities and should make rational decisions based on maximizing personal payoffs. According to the conception of Homo reciprocans, people tend to be cooperative only if their perceive partners' behaviour as fair. In the context of contemporary research, both of these theories over-simplify behaviour, since tendency to cooperate depends on differences in culture and economic development, as well as on situational rules. In the present study, the Ultimatum Game was conducted to explore students' cooperative behaviour (accepting proposals) as a response to Selfish, Equal or Altruistic offers in three conditions -'face to face', 'town to town' (long distance, with a partner from another town) or 'country to country' (with a partner from another country). This modification of standard experiment procedure was unique and allowed to examine the role of situational context. Altogether 1013 students (aged 9-19) from Poland, Spain and the United Kingdom participated in the game as acceptors. Their cooperative behaviour depended on offers made by partners. However, the patterns were moderated by game conditions: young people tended to cooperate mostly in response to equal offers and in the 'face-to-face' condition and to punish (not cooperate) partners with the same nationality ('face-to-face' or 'town-to-town' condition) for Selfish offers and foreigners ('country to country' condition) for Altruistic offers.