Abstract: User cooperation in heterogeneous networks has received great attention recently as a key solution to improve capacity in interference limited scenarios. However, nodes in heterogeneous networks are controlled by different entities and voluntary cooperation can not be assumed unless cooperation results in individual benefits. The need for studying such self-organizing and decentralized networks has resulted in the exploration of suitable game theoretic tools to analyze and predict the interactions of nodes in such networks. In this talk, we discuss the problem of cooperation in several classes of multiple access and broadcast channels from the perspective of the physical layer. Building on simple game theoretic models, we will address the question of whether cooperation among rational users can be taken for granted and characterize the regimes under which cooperation can be voluntarily assumed.