Theta Xi fraternity is founded at Rensselaer Polytechnic Institute, the only fraternity to be founded during the American Civil War.

Theta Xi (ΘΞ) is a North American Greek-letter social college fraternity. It was founded at Rensselaer Polytechnic Institute in 1864. Of all the social fraternities today, Theta Xi was the only one founded during the Civil War. Its Grand Lodge is headquartered in downtown Atlanta. Since its inception, Theta Xi has grown to include more than 60,000 initiated members. Currently, there are approximately 45 active chapters and one colony. The Theta Xi Fraternity Chapter House at Rensselaer Polytechnic Institute is listed on the National Register of Historic Places.

Rensselaer Polytechnic Institute is a private research university in Troy, New York, United States. It is the oldest technological university in the English-speaking world and the Western Hemisphere. It was established in 1824 by Stephen Van Rensselaer and Amos Eaton for the "application of science to the common purposes of life".

The American Civil War was a civil war in the United States between the Union and the Confederacy, which was formed in 1861 by states that had seceded from the Union. The central conflict leading to war was a dispute over whether slavery should be permitted to expand into the western territories, leading to more slave states, or be prohibited from doing so, which many believed would place slavery on a course of ultimate extinction.

April 29 is the 119th day of the year in the Gregorian calendar; 246 days remain until the end of the year.