Theta Xi () is a North American Greek-letter social college fraternity. It was founded at Rensselaer Polytechnic Institute (RPI) on April 29, 1864. Of all the social fraternities today, Theta Xi was the only one founded during the Civil War. Its Grand Lodge is headquartered in suburban St. Louis, Missouri. Since its inception, Theta Xi has grown to include more than 60,000 initiated members. Currently, there are approximately 50 active chapters, and 3 colonies. The Theta Xi Fraternity Chapter House at Rensselaer Polytechnic Institute is listed on the National Register of Historic Places. History Theta Xi was founded on April 29, 1864 at Rensselaer Polytechnic Institute in Troy, New York as an engineering fraternity however, now a social fraternity. Its founders were Peter Henry Fox, Ralph Gooding Packard, Christopher Champlin Waite, George Bradford Brainerd, Samuel Buel Jr., Henry Harrison Farnum, Thomas Cole Raymond, and Nathaniel Henry Starbuck. All of the original founders were members of a local fraternity called Sigma Delta, established in 1859 to rival Theta Delta Chi, which was then a secret society at RPI. Debates were common and encouraged at Sigma Delta meetings. However, on the evening of October 30, 1863, George Brainerd tendered his resignation to the society. This resignation was unanimously declined, but ultimately created a rift. Soon after, talks began circulating of affiliating with a larger organization such as Sigma Phi. However, when Sigma Phi declined to issue a charter, this only increased tensions. On March 12, 1864, voting took place for members of a new organization, and on April 1, a committee consisting of Waite, Buel, Brainerd, and Packard began preparing a new constitution. By April 6, Buel presented monograms for two new names, Theta Xi and Theta Psi. Theta Xi was chosen to avoid confusion regarding a local fraternity called Theta Psi at Yale. Within its first forty years, six chapters were established at Yale, Stevens Institute of Technology, MIT, Columbia University, Cornell University, and Lehigh University. It was not until 1905 that a westward expansion occurred with chapters at Purdue and, a month later, Washington University in St. Louis. The first west coast chapter came in 1910 at UC Berkeley, and in April 1921, the first southern chapter was founded at LSU. In 1962, talks began of folding Kappa Sigma Kappa, a smaller, struggling fraternity into Theta Xi. The merger was completed on August 20, 1962. As a direct result, several