X0 may refer to:
- SpaceShipOne flight 15P, the 2004 first privately funded human spaceflight
- X/0, a notation for the division by zero
- Turner syndrome, a disorder in which all or part of an X chromosome is absent
- X0 sex-determination system, as found in insects
- XO (disambiguation)
- X00, a popular DOS-based FOSSIL driver which was commonly used in the mid 1980s to the late 1990s
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