The Tropic of Cancer, or Northern tropic, is one of five major circles of latitude that mark maps of the Earth. It is the northernmost latitude at which the Sun can appear directly overhead at noon. This event occurs at the June solstice, when the northern hemisphere is tilted towards the sun to its maximum extent.

The Tropic of Cancer currently lies 23° 26′ 22″ north of the Equator. North of this latitude are the subtropics and Northern Temperate Zone. The equivalent line of latitude south of the Equator is called the Tropic of Capricorn, and the region between the two, centered on the Equator, is known as the Tropics.

The line is called Tropic of Cancer because when it was named the sun was in the location of the constellation of Cancer (Latin for crab) in the sky at the June solstice. However, due to the precession of the equinoxes, the sun is now in the location of the constellation of Taurus at the June solstice. The word "tropic" itself comes from the Greek tropos, meaning turn, referring to the fact that the sun appears to "turn back" at the solstices.

The position of the Tropic of Cancer is not fixed, but varies in a complex manner over time; see under circles of latitude for information.