Wikipedia: http://en.wikipedia.org/wiki/Commons 

The commons were traditionally defined as the elements of the environment - forests, atmosphere, rivers, fisheries or grazing land - that are shared, used and enjoyed by all.

Today, the commons are also understood within a cultural sphere. These commons include literature, music, arts, design, film, video, television, radio, information, software and sites of heritage. The commons can also include public goods such as public space, public education, health and the infrastructure that allows our society to function (such as electricity or water delivery systems). There also exists the ‘life commons’, e.g. the human genome.^[1]

Peter Barnes describes commons as a set of assets that have two characteristics: they are all gifts, and they are all shared. A shared gift is one we receive as members of a community, as opposed to individually. Examples of such gifts include air, water, ecosystems, languages, music, holidays, money, law, mathematics, parks and the Internet.^[2]

There are a number of important aspects that can be used to describe true commons. The first is that the commons cannot be commodified – if they are, they cease to be commons. The second aspect is that unlike private property, the commons are inclusive rather than exclusive — their nature is to share ownership as widely, rather than as narrowly, as possible. The third aspect is that the assets in commons are meant to be preserved regardless of their return of capital. Just as we receive them as shared gifts, so we have a duty to pass them on to future generations in at least the same condition as we received them. If we can add to their value, so much the better, but at a minimum we must not degrade them, and we certainly have no right to destroy them.^[2]

The public commons is commonly referred to as a place in our world that has a public good that is free for people to view and enjoy and owned by everyone who wants to be a part of it. Something as simple as water and grass that you see in the park everyday is a public common. Most times people don’t even realize that when they’re in a park that it is free. However usually in these commons it is patrolled by other people in the area and if someone were to violate the commons in anyway by littering or dumping then it would be up to people in the area to control what happens to their own place.

Some critics of Barnes say the commons are all owned by 'the people' because things like public transportation, public education and health care aren’t always available to people and are state-run services. Each of these things have a “care penalty” in which there is a certain fee or tax payable in order to use them. This type of common is provided by an infrastructure like the government but to have access to it there are taxes on families and health insurance premiums.

Another highly used public common is the Internet. The Internet is something many people have access to as a resource and a scholarly tool but is also privatized as well. This type of common is a hybrid. To gain access to the Internet a household needs an Internet service provider that they have to pay in order to get online.

There are quite a few different ways to categorize a “common” but there are public commons like parks, rivers, oceans, mountains and grasslands but there are also privatized commons that government provides and lastly the hybrid of the two where the service is free but also privatized by certain groups or individuals.

While use of the commons is generally unrestricted, there have to be certain rules in place to ensure that they are available for future generations. Overuse of the commons threatens their very existence. When considering the commons as an entity used by all, it is easy to see how there are claims that the atmosphere and skies are commons. In that case it is not a matter of what is being taken from the resources, but what is being put into those commons.

Economist Peter Barnes has proposed a sky trust to fix this problem. This idea claims that the sky belongs to all the people, and companies do not have a right to over pollute. It is a type of cap and dividend program. Ultimately the goal would be to make polluting excessively more expensive than cleaning what is being put back into the atmosphere.^[3]

The information commons may protect the community. Companies that pollute the environment release information about what they are doing. The Corporate Toxics Information Project^[4] and information like the Toxic 100, a list of the top 100 polluters,^[5] helps people know what these corporations are doing to the environment.