The monograph discusses the implications of the results of studies done in cooperative and competitive behaviour with children from grades 4,6 and 8 and the college students. The nature of cooperative and competitive behaviour has been discussed. The results on personality differences, age differences and sex differences are also discussed. Cultural differences and their implications are discussed. Results of the experiments to see the offset of communication on cooperation and the partner's behaviour on cooperation are described. Finally, a theory of cooperative behaviour, based on these results is suggested.