Nitrogen is the most abundant gas in the atmosphere: 78% of the Earth’s atmosphere is nitrogen, 21% oxygen, and 1% other gases like carbon dioxide, argon and water vapor. Nitrogen is a gas that is relatively non-reactive, non-flammable, colorless, and odorless. It is an element and its symbol is N. Nitrogen is released into the atmosphere from volcanic eruptions and when dead plants and animals decay.

During the 18th century, scientists knew that the atmosphere is composed of at least two gases; they thought that one supports life (oxygen) and the other does not support life. The Scottish scientist Daniel Rutherford, who discovered nitrogen in 1772, called it “noxious air.”

Actually, both nitrogen and oxygen support life. The circulation of nitrogen through life forms and the atmosphere is known as the Nitrogen Cycle. The cycle begins when microbes remove nitrogen from the atmosphere and use it to make nitrates and other nitrogen compounds. Plants and algae absorb these compounds into their tissues. Organisms then eat these plants and the nitrogen is absorbed and assimilated into their tissues. When living organisms die, microbes break down their tissues into ammonia (this is called ammonification) which either evaporates into the air or is used again by microbes to create nitrates. The nitrogen cycle then begins again.

Nitrogen is essential to life: all plants and animals need it to grow properly. In fact, nitrogen is a basic building block of biological molecules such as proteins. Proteins are made up of smaller molecules such as amino acids and nucleic acids (DNA, RNA). It is the fourth most abundant element in the human body.

Nitrogen is seldom sold and used as a gas. It is nearly always combined with other elements, the most common of which is hydrogen to form ammonia. Nitrogen in this state is called “fixed nitrogen” because it is fixed or attached to another element. This fixed nitrogen is the form in which nitrogen is sold and consumed.

The name nitrogen was created from the Greek words nitron genes which means nitre and forming. "Nitre" is a common name for the chemical compound potassium nitrate.

Some minerals containing nitrogen can occur in deposits large enough to be mined for their nitrogen content. Sodium and potassium nitrate mineral deposits are mined in the Atacama Desert of Chile. This, however, is a minor source of nitrogen.

Nearly all nitrogen is taken from the atmosphere. In a chemical reaction, air is made to react with hydrogen (which itself is retrieved from natural gas deposits) to make ammonia gas (NH₃). The ammonia is then combined with other molecules to create a number of end products.

China is the world’s largest ammonia producer and consumer; the United States is the world’s second largest ammonia producer and consumer. The United States produces much of the nitrogen needed for industry, all in the form of ammonia. Because natural gas is a component of ammonia, ammonia production plants are being built in locations where there are large natural gas deposits. In most cases, natural gas is less expensive in these locations. Some ammonia plants in areas with higher cost natural gas and fewer reserves, such as the United States and Europe, are being shut down. More than half of the ammonia made in the United States is made in Louisiana, Oklahoma and Texas, because these states have significant natural gas deposits. More than 80 nations produce ammonia.

Of the U.S. ammonia imports, the majority comes from Trinidad and Tobago, approximately one-third from Canada, and the rest from Mexico, Venezuela, and other nations. The United States also imports ammonia from Russia and the Ukraine.

The single greatest use of nitrogen is as fixed nitrogen in ammonia compounds. In the United States, the majority of ammonia consumption is for the production of fertilizers.

Nitrogen compounds are very explosive, and as such are used to make explosives.

Nitrogen and ammonia also have a number of other interesting uses. Liquid nitrogen is used to freeze cells in a process called cryogenics. The oil industry uses liquid nitrogen to create pressure in oil wells to force crude oil to the surface. Ammonia is used as a refrigerant, to freeze food and food products and for transporting food products. Ammonia is also important in the production of plastics, resins and synthetic fibers.