|Founded||April 29, 1864
Rensselaer Polytechnic Institute, Troy, New York
"United they Serve"
|Chapters||More than 50 in the United States|
|Patron saint||Benjamin Franklin|
|Headquarters||P.O. Box 411134
St. Louis, Missouri, USA
Theta Xi Fraternity (ΘΞ) was founded at Rensselaer Polytechnic Institute in Troy, New York on 29 April 1864. Theta Xi was originally founded as an engineering fraternity, the first-ever professional Greek letter organization. The Fraternity is governed by the National Convention and established its headquarters in St. Louis in 1924. It became a general fraternity by a five-to-one vote of the membership at the National Convention on April 9, 1926. The official motto of Theta Xi is "Juncti Juvant" which translates to "united they serve." The highest honor that a member of Theta Xi may receive is election to The Order of the Unicorn.
All of the Founding Fathers of Theta Xi were originally members of the Sigma Delta secret society. It was one of the largest secret institutions at Rensselear Polytechnic Institute (RPI) at the time in 1863. The fallout of Sigma Delta at RPI began when George Brainerd presented his resignation to the society on October 30, 1863. The society continued to descend and eventually its members became split into two sides. The eight Founding Fathers considered this unacceptable and were committed to forming a new society. On April 6, 1864, Samuel Buel, Jr. offered the idea of the new society being named Theta Xi or Theta Psi. There was knowledge of a society nearby at Yale that was called Theta Psi, and so they chose the former of the two. On the night of April 29, 1864 the eight former members of Sigma Delta met to form the founding of Theta Xi.
In its first forty years of existence, six different chapters sprang up around the area of RPI. It was not until after the turn of the century that the Fraternity started to expand westward with the Theta Chapter at Purdue and Iota Chapter at Washington University of St. Louis.
The eight fathers of Theta Xi, also known as the Alpha 8, were
A1 Peter Henry Fox
A2 Ralph Gooding Packard
A3 Christopher Champlin Waite
A4 George Bradford Brainerd
A5 Samuel Buel, Jr.
A6 Henry Harrison Farnum
A7 Thomas Cole Raymond
A8 Nathaniel Henry Starbuck
William S. Mason, considered to be one of the greatest benefactors and supporters of Theta Xi, was the main supporter of the fraternity's adoption of Benjamin Franklin as its patron saint.
National Service Projects 
At the 110th Anniversary Convention held on August 12, 1974 Theta Xi announced its adoption of the fight against Multiple Sclerosis as its National Service Project. At the 129th Anniversary Convention held on August 4–6, 1993 the fraternity announced its second alternate NSP as Habitat for Humanity.
These charities are a mainstay among all chapters of the fraternity, as well as the numerous other charities supported by individual chapters. On June 20, 1986 Theta Xi was named the Outstanding Volunteer Organization for 1985-86 by the National Multiple Sclerosis Society. Theta Xi takes exceptional pride in its members' involvement in these and other charities.
Theta Xi Foundation 
The Theta Xi Foundation was founded in 1949 in order to promote the education and growth of members of the fraternity. It is set up to aid in developing the members into responsible citizens that will contribute to the well-being of society. Contributions that mostly come from alumni and friends provide the money for the Foundation. The Foundation consists of two Funds, the Chapter Education Fund and the Unicorn Fund. The funds raised are used to sponsor several programs that are made available to undergraduate members.
Notable alumni 
List of Chapters and Colonies 
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