Skull and Bones - Vanderbilt University
- A premedical chapter of the American Medical Student Association. Not affiliated with the Order of Skull and Bones at Yale.
- http://www.vanderbilt.edu/skull_and_bones/

Sigma Phi Psi Sorority, Inc.
- Sorority for United States Armed Forces Women.
- http://www.sigmaphipsi.org/

Sigma Nu Omega Sorority Inc.
- Multi Cultural, LGBT and Allied Sorority.
- http://www.sigmanuomega.org

Sigma Phi Chi
- Christian sorority at Austin College in Sherman, Texas, founded December 17, 2001.
- http://cassidy.austincollege.edu/sigmaphichi/home.html

Sigma Beta Chi Fraternity
- Founded in 1950, Sigma Beta Chi promotes the fraternity's ideals of service, brotherhood, and cooperation. Sigma Beta Chi is St. Mary's University's oldest Fraternity.
- http://sigmabetachi.org

Sigma Phi Omicron
- Sigma Phi Omicron Fraternity was started in 1964 on the campus of the University of Massachusetts Lowell (formerly Lowell Technical Institute).
- http://www.sigo.org/

Sigma Chi Omega
- Multicultural fraternity founded at UC Santa Barbara in 1993.
- http://www.sigmachiomega.com

Sigma Dan
- An anti-fraternity, which now has expanded to a frarority (fraternity/sorority), founded on the campus of Valparaiso University.
- http://www.sigmadan.com

Sphinx
- Founded in 1900 at the University of Pennsylvania. History, member list, activities, and contact information.
- http://dolphin.upenn.edu/~pharisee/

Sigma Beta - University of New Hampshire
- Local fraternity founded in 1921 in Durham, NH.
- http://www.sigmabeta.com/

Sigma Mu Sigma
- National Fraternity founded in 1921, at Tri-State College, Angola, Indiana.
- http://www.sigmamusigma.com/

Sigma Kappa Upsilon Mu Fraternity
- A local Fraternity born in the frozen tundra of Michigan Technological University in Houghton on October 13th, 1981.
- http://www.skum.org/

Sigma Rho
- A local men's fraternity founded in 1892 at Michigan Technological University in Houghton.
- http://www.sigmarho.org/