A thirteenth is a note and an interval in music theory.
Thirteenth or 13th may also refer to:
- 13th (film), a 2016 documentary on the Thirteenth Amendment to the United States Constitution
- "The 13th", a song from Wild Mood Swings by The Cure
- "The Thirteenth" (Orange Is the New Black), a 2019 television episode
- Thirteenth, Italian fairy tale from Sicily