Tragedy of the commons

A situation in which individuals acting in their own interest deplete or degrade a shared resource, harming the group that depends on it.

Common-pool resource: A resource that is difficult to exclude people from using and whose use by one person reduces what remains for others. The tragedy arises when many users draw from this subtractable resource without effective limits.
Overfishing: Fishing at a rate that reduces fish populations faster than they can replenish. Competing fleets can gain from larger catches while collectively exhausting a fishery.
William Forster Lloyd: A British economist whose 1833 lectures described how shared pasture could be overused by individual herders. His pasture example is an early formulation of the problem later known by this name.
Ostrom's design principles: A set of institutional features associated with durable community governance of common-pool resources. These principles show how users can organize to avoid the predicted collapse.
Enclosure movement: The long historical conversion of English common lands into privately held property, especially from the fifteenth through nineteenth centuries. Arguments about preventing overuse have often been used to justify enclosing shared land.
Externality: A cost or benefit of an activity that falls on people outside the decision-maker's transaction. Users can impose depletion costs on others without bearing the full consequences of their choices.
Groundwater depletion: The long-term reduction of groundwater reserves when extraction exceeds replenishment. Wells drawing from a shared aquifer can lower water levels for every user.
Garrett Hardin: An American ecologist who popularized the phrase “tragedy of the commons” in a 1968 essay. Hardin recast the dilemma as a warning about population growth and unmanaged shared resources.
Common property: A property regime in which a defined group holds rights to manage and use a resource collectively. A governed commons is not equivalent to unrestricted open access.
Environmental governance: The institutions, rules, and practices through which societies make and enforce decisions about the environment. The concept directs attention toward who sets resource rules and how those rules are enforced.

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