This experiment investigates contests between groups. Each group has one strong player,with a higher valuation for the prize, and two weak players, with lower valuations. Incontests where individual efforts are perfect substitutes, all players expend significantlyhigher efforts than predicted by theory. In best-shot contests, where group performancedepends on the best performer, most of the effort is expended by strong players while weakplayers free-ride. In weakest-link contests, where group performance depends on the worstperformer, there is almost no free-riding and all players expend similar positive effortsconforming to the group Pareto dominant equilibrium.