In the past, very little research has attempted to illuminate the relationships between social or economic inequalities, institution intervention, and ecological outcomes of common resources. The purpose of this study is to examine the effects of inequalities within (intra-group) and between (inter-group) groups on forest commons. The authors gathered 228 cases from six countries (India, Nepal, Kenya, Uganda, Mexico, Bolivia) ranging from 1994 to 2002. The study revealed that both intra- and inter-group inequalities have negative effects upon forest commons, and effective institutional involvement may help mitigate the negative effects of inter-group inequalities. These findings support the argument for addressing social and economic disparities as an effective means in improving the ecological sustainability of forest commons.