A green belt or greenbelt is a policy and land use designation used in land use planning to retain areas of largely undeveloped, wild, or agricultural land surrounding or neighbouring urban areas. Similar concepts are greenways or green wedges which have a linear character and may run through an urban area instead of around it. In essence, a green belt is an invisible line designating a border around a certain area, preventing development of the area and allowing wildlife to return and be established.
In those countries which have them, the stated objectives of green belt policy are to:
- Protect natural or semi-natural environments;
- Improve air quality within urban areas;
- Ensure that urban dwellers have access to countryside, with consequent educational and recreational opportunities; and
- Protect the unique character of rural communities that might otherwise be absorbed by expanding suburbs.
The green belt has many benefits for people:
- Walking, camping, and biking areas close to the cities and towns.
- Contiguous habitat network for wild plants, animals and wildlife.
- Cleaner air and water
- Better land use of areas within the bordering cities.
The effectiveness of green belts differs depending on location and country. They can often be eroded by urban rural fringe uses and sometimes, development 'jumps' over the green belt area, resulting in the creation of "satellite towns" which, although separated from the city by green belt, function more like suburbs than independent communities.
The Old Testament outlines a proposal for a green belt around the Levite towns in the Land of Israel Moses Maimonides expounded that the greenbelt plan from the Old Testament referred to all towns in ancient Israel. In the 7th century, Muhammad established a green belt around Medina. He did this by prohibiting any further removal of trees in a 12-mile long strip around the city. In 1580 Elizabeth I of England banned new building in a 3-mile wide belt around the City of London in an attempt to stop the spread of plague. However, it was possible to buy dispensations which reduced the effectiveness of the proclamation.
In modern times, green belt policy was pioneered in the United Kingdom in the 1930s after pressure from the CPRE and various other organizations. There are fourteen green belt areas, in the UK covering 16,716 km², or 13% of England, and 164 km² of Scotland; for a detailed discussion of these, see Green belt (UK). Other notable examples are the Ottawa Greenbelt and Golden Horseshoe Greenbelt in Ontario, Canada. Ottawa's 20,350 hectare greenbelt is managed by the National Capital Commission (NCC). The more general term in the U.S. is green space or greenspace, which may be a very small area such as a park.
The concept of "green belt" has evolved in recent years to encompass not only "Greenspace" but also "Greenstructure", taking into account all urban greenspaces, an important aspect of sustainable development in the 21st century. The European Commission's COST Action C11 (COST - European Cooperation in Science and Technology) is undertaking "Case studies in Greenstructure Planning" involving 15 European countries.
An act of the Swedish parliament from 1994 has declared a series of parks in Stockholm and the adjacent municipality of Solna to its north a "national city park" called Ekoparken (the "Eco park"; it stretches from the parks surrounding the royal palaces of Ulriksdal and Haga in Solna, through the Brunnsviken area, down to the former royal hunting grounds of North and South Djurgården).
The difference/contrarian interpretation of the green belt's effects/motivation (for example, suggested by economist Tim Harford ) is that a green belt is created by residents to preserve the bourgeois status quo of those already living within the zone, and especially the advantage of landlords who profit from a scarcity of housing (see above, "preserving the character of rural communities"). In this interpretation, the stated motivation and benefits of the green belt are well-intentioned (public health, environment), but these benefits accrue as intentioned or claimed (for example, critics such as Mark Pennington  claim that only a small fraction of the population ever sets foot on the green belt for leisure purposes, and they claim that a green belt is not strongly causally linked to clean air and water). Rather, the ultimate result of the decision to green belt a city is to maintain the middle class status quo,  thus exacerbating high housing prices by concentrating demand within the zone and stifling competitive forces in general.
Another area of criticism comes from the fact that, since a greenbelt does not extend indefinitely outside a city, it might spur the growth of areas much further away from the city core than if it had not existed, thereby actually increasing urban sprawl. Examples commonly cited are the Ottawa suburbs of Kanata and Orleans, both of which are outside the city's greenbelt, and are currently undergoing explosive growth (see Greenbelt (Ottawa)). This can lead to other problems, as residents of these areas have further to commute to work (if they seek employment in city) and little access to public transport. It also means people will commute through the green belt, an area not designed to cope with high levels of transportation. Not only is the merit of a green belt apparently subverted, but the green belt may heighten the problem and make the city unsustainable.
There are many examples whereby the actual effect of green belts is to act as a land reserve for future freeways and other highways. Examples include sections of the 407 highway north of Toronto and the Hunt Club Rd / Richmond Rd. south of Ottawa. Whether they are originally planned as such, or the result of a newer administration taking advantage of land that was left available by its predecessors is debatable.
In Britain, greenbelt barriers to urban expansion have been criticised as one of several protectionist political-economic barriers to housebuilding with negative effects on the supply, cost/prices, and quality of new homes. Critics argue that the greenbelts actually defeat their own stated objective of saving the countryside and open spaces. By preventing existing towns and cities from extending normally and organically, they result in more land-extensive housing developments further out – i.e., the establishment beyond the greenbelts of new communities with lower building densities, their own built infrastructure and other facilities, and greater dependence on cars and commuting, etc. Meanwhile, valuable urban green space and brownfield sites best suited to industry and commerce are lost in existing conurbations as more and more new housing is crammed into them.
Notable green belts 
- Adelaide's Central Business District is completely encircled by the Adelaide Parklands, as was initially planned in 1837.
- The Nillumbik Shire Council which is located approximately 30 km (19 miles) north-east of Melbourne is considered as "The Green Wedge Shire" because of the agreement with the Victorian Government which prevents high-density infrastructure to be built.
- The São Paulo City Green Belt Biosphere Reserve - GBBR, an integral part of the Atlantic Forest Biosphere Reserve, was created in 1994 stemming from a people's movement that collected 150 thousand signatures. It extends throughout 73 municipalities including São Paulo metro and the Santos area. With approximately 17,000 km², it is inhabited by about 23 million people, corresponding to more than 10% of the country's total population in an area equivalent to 2 thousandth of the Brazilian territory. There are over 6,000 km² of forests and other Atlantic Forest ecosystems at the Reserve, one of the planet's most threatened biomes. In addition to a spectacular biological diversity, the GBBR's ecosystems render valuable ecosystem Services.
- Ottawa Greenbelt - Surrounds the Capital city of Ottawa
- Greenbelt (Golden Horseshoe), is a 7300 km² band of land that encompasses the rural and agricultural land surrounding the Greater Toronto Area and Niagara Peninsula, and parts of the Bruce Peninsula. It’s the largest greenbelt in the world and larger than Canada's smallest province - PEI. Most of the land consists of the Oak Ridges Moraine, an environmentally sensitive land that is a major aquifer for the region, and the Niagara Escarpment, a UNESCO Biosphere Reserve. In an effort to restrain urban sprawl that has encroched on these lands, the Ontario government created the Greenbelt Act in February 2005 to protect this greenspace from all future development, with the exception of limited agricultural use.
- British Columbia - the Agricultural Land Reserve protects agricultural land throughout this mountainous province from urban development, including around Vancouver. This protection is strict and urban development of agricultural land is only allowed if no reasonable alternative exists. However, it does not protect non-agricultural land, particularly hillsides, leading to substantial, and highly visible, leapfrog-type hillside sprawl.
- Quebec - The Commission de protection du territoire agricole du Quebec asserts its mission, namely to keep a territory (the agricultural zones) that is favorable for the practice and the development of agricultural activities. In so doing, the commission safeguards the agricultural territory and helps make its protection a local priority. The agricultural zones cover an area of 63 000 square kilometres in 952 local municipalities.
- The Greater Santo Domingo has a Greenbelt (Santo Domingo Greenbelt) project surrounding the whole D.N. It is composed of the National botanical Garden, Mirador Del Norte, Mirador del Este, and other parks surrounding the area from its outer municipios. It has largely been affected by uncontrolled urbanization, but other parts remain unaffected.
- European Green Belt
- Banjica Forest, Belgrade
- Stockholm Eco park
- German Green Belt
- Coulée verte du sud parisien
- Coulée verte du nord parisien
- Promenade plantée
- Vienna Woods, Austria
- Dunedin's Town Belt is one of the world's oldest green belts, having been planned at the time of the city's rapid growth during the Otago Gold Rush of the 1860s. It surrounds the city centre on three sides (the fourth side being the city's harbour).
- Islamabad, often called the "green city," is known for its green belts found on most roadsides which are often decorated and filled with various flora.
- Makati City's green belt is very green yet full of malls and modern structures.
- Bangkok's Bang Krachao Green Area located inside the curve of Chao Phraya River is considered a green area with authority control over the urbanization. Today it is a popular spot for tourism and cycling. The area is located within the boarder of Bangkok Province and Samut Sakorn Province.
- The Metropolitan Green Belt (5,133 km²)
- The North West Green Belt (2,578 km²)
- South and West Yorkshire Green Belt (2,556 km²)
- West Midlands Green Belt (2,315 km²)
- The U.S. states of Oregon, Washington and Tennessee require cities to establish urban growth boundaries (UGBs).
- Notable US cities which have adopted UGBs include Portland, Oregon; Twin Cities, Minnesota; Virginia Beach, Virginia; Lexington, Kentucky; Miami-Dade county.
- More than 20 cities in the San Francisco Bay Area have UGBs (see Greenbelt Alliance, a Bay Area organization that has been involved in establishing these boundaries).
- Staten Island Greenbelt
- Barton Creek Greenbelt, Austin
- Ann Arbor, Michigan is acquiring conservation easements on agricultural land around the city without the establishment of an urban growth boundary. While the city's initial plan did not include the participation of surrounding townships, at least four townships have participated directly or have initiated their own efforts to protect agricultural land surrounding the city.
- Boise Greenbelt, Boise, Idaho
- "The Jungle", Seattle
- Boston's Emerald Necklace is halfway between a green belt and a greenway, nearly ringing central Boston. The final link in the chain, the Dorchesterway, was never constructed.
See also 
- Community separator
- Conservation movement
- Development Supported Agriculture
- Land use planning
- Prime farmland
- Urban growth boundary
- Urban rural fringe
- Urban sprawl
- Numbers 35:1-5
- Mishna Torah, Zeraim, Shmittah & Yovel 13:4-5
- Iqbal, Munawwar (2005). Islamic Perspectives on Sustainable Development. p. 27. Published jointly by Palgrave Macmillan, University of Bahrain, and Islamic Research and Training Institute.
- Halliday, Stephen (2004). Underground to Everywhere. Sutton Publishing Limited. p. 118. ISBN 0-7509-3843-9.
- National Capital Commission. "National Capital Commission :: The National Capital Greenbelt :: History and Culture." National Capital Commission - Commission De La Capitale Nationale (NCC-CCN). 07 Dec. 2007. NCC-CCN. Accessed 28 June 2008, unavailable February, 2013.
- How Much Open Space is Enough?" St. Paul Pioneer Press (MN) - April 22, 2007 - A1 MAIN
- Political Barriers To Housebuilding In Britain: A Critical Case Study Of Protectionism & Its Industrial-Commercial Effects, Industrial Systems Research/ Google Books, new edition 2002. Chapter two: “Greenbelt Barriers To Urban Expansion.” ISBN 978-0-906321-21-8