publicgood

A public good is a good or service that is non-excludable and non-rivalrous in consumption. Non-excludable means that once provided, no one can be effectively prevented from using it. Non-rivalrous means that one person’s use does not diminish availability for others. Because of these properties, markets often underprovide public goods, since individuals have an incentive to free-ride on others’ contributions.

Common examples include national defense, clean air, basic scientific knowledge, street lighting, and public parks. Public goods can create positive externalities and may generate social benefits that extend beyond the individuals who consume them. Their provision is frequently funded or organized by the government or through collective action, though private and philanthropic initiatives can also contribute.

Public goods are often discussed as pure public goods or as impure/public goods. Pure public goods are non-excludable and non-rivalrous, while impure public goods have some degree of excludability or rivalry (such as education, healthcare, or infrastructure). In many cases, a mix of public and private provision exists, with governments or cooperatives supplying the portion that markets fail to provide efficiently.

Economic analysis of public goods uses the Samuelson condition, which states that the sum of all individuals’ marginal valuations of the public good should equal its marginal cost for efficient provision. In practice, measuring valuations is difficult, so provision relies on political processes, taxation, and policy design. Global public goods, including climate stability and international health, highlight coordination challenges beyond national borders.