Undecidable may refer to:
- In mathematics and logic
- Undecidable problem - a decision problem which no algorithm can decide
- "Undecidable" is sometimes used as a synonym of "independent", where a formula in mathematical logic is independent of a logical theory if neither that formula nor its negation can be proved within the theory
- Other uses
- Undecidable figure
- Undecidable language
- Undecidable set
- Also
- List of undecidable problems