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The meridian was agreed upon in October 1884. At the behest of the President of the United States of America, 41 delegates from 25 nations met in Washington, D.C., USA for the International Meridian Conference.

At the conference the following important principles were established:

1. It was desirable to adopt a single world meridian to replace the numerous ones already in existence.
2. The meridian passing through the principal transit instrument at the Observatory at Greenwich was to be the "initial meridian".
3. That all longitude would be calculated both east and west from this meridian up to 180°.
4. All countries would adopt a universal day.
5. The universal day would be a mean solar day, beginning at the mean midnight at Greenwich and counted on a 24-hour clock.
6. That nautical and astronomical days everywhere would begin at mean midnight.
7. All technical studies to regulate and extend the application of the decimal system to the division of time and space would be supported.

Resolution 2, fixing the meridian at Greenwich, was passed 22-1 ( San Domingo, now Haiti, voted against); France and Brazil abstained. The French did not adopt the Greenwich meridian until 1911.

The international date line (the jagged red line down the right side of the image to the right) is on the opposite side of the world from the Prime Meridian.

Previously, the meridian of the Canarian island El HierroEl Hierro a Spanish island, is the smallest and furthest south and west of the Canary Islands, in the Atlantic Ocean off the coast of Africa. It is situated at 27°45' north, 18°00' west. Like the rest of the chain, the island is sharply mountainous. It ha was used by most of the navies of continental Europe. It was conventionally defined as the meridian 20 degrees west from ParisEiffel Tower has become the symbol of Paris throughout the world. Paris is the capital and largest city of France. The city is built on an arc of the River Seine, and is thus divided into two parts: the Right Bank to the north and the smaller Left Bank to (17° 39' 46" west of Greenwich).

Other prime meridians used previously include RomeRome ( Italian and Latin Roma is the capital city of Italy, and of its Lazio region. It is located on the lower Tiber river, near the Mediterranean Sea, at 41°50'N, 12°15'E. The Vatican City State, a sovereign enclave within Rome, is the seat of the Roman (12° 27' 08.04" east of Greenwich), CopenhagenCopenhagen Kobenhavn in Danish) is the capital of Denmark. The contemporary Danish name for the city is a corruption of the original designation for the city Kobmandshavn meaning Merchants' Harbour. The English name Copenhagen is derived from the German n, JerusalemCapitals in Asia For alternate uses see Jerusalem (disambiguation Jerusalem ( Modern Hebrew: Yerushalayim Biblical Hebrew: Arabic: al-Quds see also Names of Jerusalem) is an ancient Middle Eastern city of key importance to the religions of Judaism, Christ, Saint PetersburgSaint Petersburg ( Russian: English transliteration: Sankt-Peterburg), colloquially known as (transliterated "Piter"), formerly known as Leningrad (, 1924- 1991) and Petrograd (, 1914- 1924), is a city located in Northwestern Russia on the Gulf of Finland (Pulkovo meridian, 30° 19'; 42.09" east of Greenwich), PisaThis article is about Pisa in Italy. For other places of the same name, see Pisa (disambiguation). Pisa (population 90,000) is a city in Tuscany, Italy at the mouth of the river Arno on the Mediterranean. By far the best known sight in Pisa is the famous, ParisEiffel Tower has become the symbol of Paris throughout the world. Paris is the capital and largest city of France. The city is built on an arc of the River Seine, and is thus divided into two parts: the Right Bank to the north and the smaller Left Bank to (2° 20' 14" east of Greenwich), and PhiladelphiaAlternate meanings: Philadelphia (disambiguation Philadelphia is the fifth-largest city in the United States and the largest city in Pennsylvania, occupying all of Philadelphia County . As of the 2000 census, the population was 1,517,550, but a July 1, 20.

With respect to other solid celestial bodies, prime meridians are likewise arbitrarily defined. The prime meridian of Earth's moon lies directly in the middle of the face of the moon visible from earth and passes near the crater Bruce. The prime meridian of the planet Mars is defined by the crater Airy-0.