The 40th parallel north is a circle of latitude that is 40 degrees north of the Earth's equatorial plane. It crosses Europe, the Mediterranean Sea, Asia, the Pacific Ocean, North America, and the Atlantic Ocean.

At this latitude the sun is visible for 15 hours, 1 minute during the summer solstice and 9 hours, 20 minutes during the winter solstice. On 21 June, the maximum altitude of the sun is 73.83 degrees and 26.17 degrees on 21 December.

Around the world

Starting in Spain at the Prime Meridian and heading eastwards, the parallel 40° north passes through:

United States

The parallel 40° north forms the boundary between the states of Kansas and Nebraska. On 30 May 1854, the Kansas–Nebraska Act created the Territory of Kansas and the Territory of Nebraska divided by the parallel 40° north. Both territories were required to determine for themselves whether to permit slavery. Open conflict between free-state and pro-slavery forces in the Kansas Territory was one of the root causes of the American Civil War.

40th parallel may refer to: