In economics, a public good (also referred to as a social good or collective good) is a good that is both non-excludable and non-rivalrous. For such goods, users cannot be barred from accessing or using them for failing to pay for them. Also, use by one person neither prevents access of other people nor does it reduce availability to others. Therefore, the good can be used simultaneously by more than one person. This is in contrast to a common good, such as wild fish stocks in the ocean, which is non-excludable but rivalrous to a certain degree. If too many fish were harvested, the stocks would deplete, limiting the access of fish for others. A public good must be valuable to more than one user, otherwise, the fact that it can be used simultaneously by more than one person would be economically irrelevant.

Capital goods may be used to produce public goods or services that are "...typically provided on a large scale to many consumers." Unlike other types of economic goods, public goods are described as “non-rivalrous” or “non-exclusive,” and use by one person neither prevents access of other people nor does it reduce availability to others. Similarly, using capital goods to produce public goods may result in the creation of new capital goods. In some cases, public goods or services are considered "...insufficiently profitable to be provided by the private sector.... (and), in the absence of government provision, these goods or services would be produced in relatively small quantities or, perhaps, not at all."

Public goods include knowledge, official statistics, national security, common languages, law enforcement, public parks, free roads, television and radio broadcasts. Additionally, flood control systems, lighthouses, and street lighting are also common social goods. Collective goods that are spread all over the face of the earth may be referred to as global public goods. This is not limited to physical book literature, but also media, pictures and videos. For instance, knowledge is well shared globally. Information about men, women and youth health awareness, environmental issues, and maintaining biodiversity is common knowledge that every individual in the society can get without necessarily preventing others access. Also, sharing and interpreting contemporary history with a cultural lexicon, particularly about protected cultural heritage sites and monuments are other sources of knowledge that the people can freely access.

Public goods problems are often closely related to the "free-rider" problem, 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; exclusion mechanisms include toll roads, congestion pricing, and pay television with an encoded signal that can be decrypted only by paid subscribers.

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.