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Ownership rights often emerge from adversarial interactions in which agents make claims and defend them from the appropriation efforts of others. In this paper, we first offer an overview of the theoretical literature on this issue. We systematize the existing models by classifying them into two families and show that they can explain the emergence of classic types of ownership rights. We then explore a new model where agents can become the sole owner of a commonly owned production resource through an exclusion contest. We show that while overexploitation when it comes to common ownership is severe enough relative to the returns to scale of conflict activities, private ownership emerges out of conflict. Inequality makes private ownership more likely to emerge. Finally, we describe the set of common ownership regimes that are Pareto efficient and immune to conflict. The results show that sharing outputs proportionally, in terms of how much labor has been done, makes common ownership more resilient to conflict when inequality is higher.