Saint Elmo or St. Elmo may refer to:
- Erasmus of Formia or Saint Elmo (died 303), patron saint of sailors
- Peter González or Saint Elmo (1190–1246), Castilian Dominican friar and priest
- St. Elmo Brady (1884–1966), first African American to obtain a Ph.D. in chemistry in the United States
United States
- St. Elmo, Alabama
- Saint Elmo, Colorado
- St. Elmo (Columbus, Georgia), a historic residence
- St. Elmo, Illinois
- St. Elmo, Louisiana, a community in Ascension Parish, Louisiana
- St. Elmo, Michigan, a community in Midland County
- St. Elmo Historic District (Chattanooga, Tennessee)
- St. Elmo Steak House, a restaurant in Indianapolis, Indiana, U.S.
- St. Elmo, a nickname for the fraternity of Delta Phi
- St. Elmo Society, a senior secret society at Yale University
- St. Elmo Hall, a building formerly owned by the St. Elmo Society at Yale University
- St. Elmo Hall, a nickname for the fraternity of Delta Phi