Indeterminacy or underdeterminacy may refer to:
- Indeterminacy in computation (disambiguation)
- aleatoric music and indeterminacy in music.
- Statically indeterminate
- Indeterminacy (literature) a literary term
- In set theory and game theory, the opposite of determinacy
- Underdetermined system
In law:
- Indeterminacy debate in legal theory
- Underdeterminacy (law)
In linguistics:
- Indeterminacy of translation
- Referential indeterminacy
In philosophy:
- Indeterminacy (philosophy)
- Indeterminism, the belief that not all events are causally determined
- Deterministic system (philosophy)
- Philosophy of science#Indeterminacy of theory under empirical testing
- Underdetermination
In physics:
- Quantum indeterminacy
- Uncertainty principle
- Scientific determinism