Sigma Xi, The Scientific Research Honor Society (ΣΞ) ( ) is an international non-profit honor society for scientists and engineers. Sigma Xi was founded at Cornell University by a faculty member and graduate students in 1886 and is one of the oldest honor societies. Membership in Sigma Xi is by invitation only, where members nominate others on the basis of their research achievements or potential. The society was a founding member of the Association of College Honor Societies in 1925, but withdrew in 1933 and, much later, helped form the Honor Society Caucus.