The Mariana Trench is the deepest known submarine trench, and the deepest location in the Earth itself. It is located in the floor of the western North Pacific Ocean, to the east of the Mariana Islands at 11"21' North latitude and 142" 12' East longitude, which is near Japan.

The trench has a maximum depth of 10,911 m (35,797 feet) below sea level. It was first surveyed in 1951 by the British navy vessel, Challenger II, which gave its name to the deepest part of the trench, the Challenger Deep. In 1984 the Japanese sent a highly specialized survey vessel out to the Mariana Trench and collected data using a narrow, multi-beam echo sounder. The most accurate measurement on record was taken by another Japanese probe, "Kaiko", on March 24, 1995.

The trench is the boundary where two tectonic plates meet, a subduction zone where the Pacific Plate is being subducted under the Philippine Plate. The bottom of the trench is further below sea level than Mount Everest is above sea level.

In an unprecedented dive, the U.S. Navy bathyscaphe Trieste reached the bottom at 1:06 pm on January 23, 1960 with U.S. Navy Lt. Don Walsh and Jacques Piccard. Iron shot was used for ballast, with gasoline for buoyancy. The onboard systems indicated a depth of 37,800 ft (11,521 m), but this was later revised to 35,813 ft (10,916 m). At the bottom Walsh and Piccard were surprised to discover soles or flounder about one foot (30 cm) long, as well as shrimp. According to Piccard, "The bottom appeared light and clear, a waste of firm diatomaceous ooze".

At the bottom of the Mariana Trench, water exerts a pressure of 1086 bar (108.6 MPa or 15,751 psi).