The Western Hemisphere is a geographical term   for the half of Earth which lies west of the prime meridian (which crosses Greenwich, London, United Kingdom) and east of the antimeridian. The other half is called the Eastern Hemisphere. 
The Western Hemisphere consists of the Americas, the western portions of Europe and Africa, the extreme eastern tip of Siberia ( Russia), numerous territories in Oceania, and a portion of Antarctica, while excluding some of the Aleutian Islands to the southwest of the Alaskan mainland.
The center of the Western Hemisphere is located in the Pacific Ocean at the intersection of the 90th meridian west and the Equator, among the Galápagos Islands. The nearest land is Genovesa Island at .
In an attempt to define the Western Hemisphere as the parts of the world which are not part of the Old World, there also exist projections which use the 20th meridian west and the diametrically opposed 160th meridian east to define the hemisphere.  This projection excludes the European and African mainlands and a small portion of northeast Greenland, but includes more of eastern Russia and Oceania.
Below is a list of the sovereign states which are in both the Western and Eastern Hemispheres on the IERS Reference Meridian, in order from north to south:
- Denmark (due to Greenland and the Faroe Islands; mainland Denmark lies entirely in the Eastern Hemisphere).
- Norway (due to Jan Mayen; mainland Norway lies entirely in the Eastern Hemisphere).
- United Kingdom, passing through Greenwich, London. Most of the country is in the Western Hemisphere.
- France, passing through Puynormand ( Gironde.) About 1/3 of the country, including cities like Nantes or Bordeaux, as well as the departments of Guadeloupe, Martinique, and French Guiana lie in the Western Hemisphere.
- Spain, passing through Castelló de la Plana ( Valencian Community.) Most of Spain, including the capital Madrid, the Canary Islands and the southern half of its Mediterranean territorial waters, lies in the Western Hemisphere. Spanish, Moroccan and Algerian Mediterranean waters are the only part of the Mediterranean Sea located in the Western Hemisphere.
- Algeria, passing through Stidia. About 1/4 of the country including Oran, Algeria's second largest city, is in the Western Hemisphere.
- Mali, passing through the municipal area of Gao. Most of Mali, including the capital Bamako, lies in the Western Hemisphere.
- Burkina Faso, passing through Lalgaye. Most of the country, including the capital Ouagadougou, is in the Western Hemisphere.
- Ghana, passing through Tema. Most of Ghana, including the capital Accra, lies in the Western Hemisphere.
- Togo, passing near Tami ( Savanes Region).
Below is a list of the sovereign states which are in both the Western and Eastern Hemispheres along the 180th meridian, in order from north to south. With the exception of the United States ( Wake Island), all of them are located on just one side of the International Date Line, which is curved around them.
- Russia ( Siberia, Far East)
- United States ( United States Minor Outlying Islands, Aleutian Islands, Northern Mariana Islands, Guam)
- New Zealand ( Kermadec and Chatham Island groups are east of the 180th meridian)
One sovereign state has territory on both hemispheres, but neither the prime meridian nor the 180th meridian passes through its territory:
- Netherlands (The islands of the Caribbean Netherlands lie entirely within the Western Hemisphere while the European Netherlands lies entirely in the Eastern Hemisphere.)
The following countries and territories lie outside the Americas yet are entirely/mostly or partially within the Western Hemisphere:
- Olson, Judy M (1997), "Projecting the hemisphere", in Robinson, Arthur H; Snyder, John P (eds.),
Matching the map projection to the need, Bethesda, MD: Cartography and Geographic Information Society, American Congress on Surveying and Mapping.
- "Western Hemisphere", Merriam-Webster's Geographical Dictionary (3rd ed.), Springfield, Massachusetts: Merriam-Webster, 2001, p. 1294.
Oxford Dictionary of English (2nd ed.), London, UK:
Oxford University Press, 2006, p. 2001
- "Western /western%20hemisphere", Merriam Webster's Online Dictionary (based on Collegiate vol., 11th ed.), Springfield, MA: Merriam-Webster, 2006
- "Western Hemisphere", Britannica.com
- Bureau of Western Hemisphere Affairs, United States Department of State.
- Western Hemisphere, United States Department of the Treasury.
- Western Hemisphere, Office of the United States Trade Representative.
- Joe Biden: The Western Hemisphere Needs U.S. Leadership, Americas Quarterly, 17 December 2018.
- Western Hemisphere, United States Department of Justice.
- Western Hemisphere, United States Department of Agriculture.
- Western Hemisphere, United States Fish and Wildlife Service.
- Western Hemisphere, Fulbright Program.
- "Informe científico que estudia el Aconcagua, el Coloso de América mide 6960,8 metros" [Scientific Report on Aconcagua, the Colossus of America measures 6960,8m] (in Spanish). Universidad Nacional de Cuyo. 2012. Archived from the original on September 8, 2012. Retrieved September 3, 2012.
- Media related to Western Hemisphere at Wikimedia Commons