Since I was invited to speak about common-property arrangements in the management of water resources, I shall begin with a description of common-property arrangements. I will then turn to the relationship between the common property and regulatory-agency approaches to water resource management, addressing both its empirical manifestations and some theoretical bases for understanding them. Then I will consider the relationship between common-property and private-property or market arrangements, again analyzing that relationship from empirical and theoretical perspectives. When I use examples or illustrations in this brief presentation, they will have to do with groundwater basins in the United States since those are the empirical cases with which I am familiar. And throughout my remarks, I will be applying the analytical approach of institutional rational-choice analysis, and restating the work of many scholars who have worked in the field of common-property resources.