We consider network games in which players simultaneously form partnerships and

choose actions. Players are heterogeneous with respect to their action preferences. We

characterize pairwise Nash equilibria for a large class of games, including coordination

and anti-coordination games, varying the strength of action preferences and the size

of the linking cost. We find that, despite the symmetry and simplicity of the setting,

quite irregular network structures can arise in equilibrium, implying that heterogeneity

in players' action preferences may already explain a large part of observed irregularity

in endogenously formed networks.