Quaternion can refer to:
Mathematics
- Quaternions, a number system that extends the complex numbers.
- Quaternion rotation, systems for describing how rotation groups and quaternions interact
- Quaternion group (Q<sub>8</sub>), a non-abelian group of order 8 that describes the quaternions
Symbols
- Imperial quaternions (heraldry of the Holy Roman Empire)
- Quaternion Eagle
Military uses
- A group of four soldiers in the Roman legion
- A fireteam
Other
- Quaternion (gathering), four folded sheets as a unit in bookbinding
- Quaternion (poetry), a style of poetry with four parts