Theta Xi (ΘΞ) was founded at Rensselaer Polytechnic Institute in Troy, New York on 29 April 1864. Theta Xi Fraternity was originally founded as an engineering fraternity, the first professional fraternity. It became a general fraternity by a five-to-one vote of the membership at the National Convention on April 9, 1926.

In addition to philanthropies adopted by individual chapters, Theta Xi supports two national service projects, for the fight against Multiple Sclerosis and Habitat for Humanity.

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