- The Western Front: This was the main theater of operations, stretching from the North Sea to the Swiss border. The fighting here was intense and bloody, with millions of casualties.
- The Eastern Front: This front stretched from the Baltic Sea to the Black Sea. The fighting here was also intense, but it was more fluid than on the Western Front, with large-scale advances and retreats.
- The Southern Front: This front included fighting in the Balkans, the Middle East, and North Africa. The fighting here was less intense than on the other fronts, but it was still significant.
- The Naval Front: The naval front included fighting in the Atlantic Ocean, the Pacific Ocean, and the Indian Ocean. The fighting here was less intense than on the other fronts, but it was still significant, especially in the Atlantic, where German U-boats sank thousands of Allied ships.
Other fronts of World War I included:
- The Italian Front: This front included fighting in the Alps and along the Isonzo River. The fighting here was intense, but it was stalemated for much of the war.
- The Romanian Front: This front included fighting in Romania. The fighting here was also intense, but it ended with a Romanian defeat in 1916.
- The Caucasus Front: This front included fighting in the Caucasus Mountains. The fighting here was intense, but it ended with a Russian victory in 1917.
- The Mesopotamian Front: This front included fighting in Mesopotamia (now Iraq). The fighting here was intense, but it ended with a British victory in 1918.