Theta Delta Sigma Society, Inc. (ΘΔΣ) is a national gender inclusive multicultural fraternal organization founded in 2001 at the University at Buffalo (SUNY).

[1] Theta Delta Sigma is a non-partisan and non-sectarian organization that has been "a partner in the values-based fraternal movement".

The society's first service commitment was a volunteer babysitting program that provided low-income families with a free and dependable babysitter.

This service has been discontinued; however, Theta Delta Sigma continues to be involved in the lives of youth through association with Big Brothers Big Sisters of America, Boys & Girls Clubs of America, Make-A-Wish Foundation, Toys for Tots, UNICEF, and Variety Club International For one weekend each spring, all chapters and colonies hold concurrent service projects built around service to disadvantaged youth.

Theta Delta Sigma partners with the Phi Mu Women’s Fraternity for National Ritual Celebration Week, an annual initiative to encourage members of fraternities and sororities to reflect on the ritual that makes each organization unique.