The 39th parallel north is a circle of latitude that is 39 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 14 hours, 54 minutes during the summer solstice and 9 hours, 26 minutes during the winter solstice.

Daylight along the 39th parallel north falls under 10 hours a day starting on 18 November and returns to over ten hours a day beginning 24 January. The growth of crops and other plants is considerably slowed during this period of reduced sunlight.

In the United States, the eastern boundary of the state of California was defined as following the 120th meridian west south from the 42nd parallel north to its intersection with the 39th parallel north, beyond which it follows a diagonal line to where the Colorado River crosses the 35th parallel north. The intersection of the 120th meridian and 39th parallel is in Lake Tahoe.