Public Good

In economics, a public good is a good that is both non-excludable and non-rivalrous in that individuals cannot be effectively excluded from use and where use by one individual does not reduce availability to others. Examples of public goods include fresh air, knowledge, lighthouses, national defence, flood control systems and street lighting. Public goods that are available everywhere are sometimes referred to as global public goods.

Many public goods may at times be subject to excessive use resulting in negative externalities affecting all users; for example air pollution and traffic congestion. Public goods problems are often closely related to the "free-rider" problem or the tragedy of the commons, in which people not paying for the good may continue to access it. Thus, the good may be under-produced, overused or degraded. Public goods may also become subject to restrictions on access and may then be considered to be club goods or private goods; exclusion mechanisms include copyright, patents, congestion pricing, and pay television.

Uncoordinated markets driven by self-interested parties may be unable to provide these goods. There is a good deal of debate and literature on how to measure the significance of public goods problems in an economy, and to identify the best remedies.