Lists of unsolved problems
- Cold case
- List of NP-complete problems
- List of PSPACE-complete problems
- List of ciphertexts
- List of conjectures
- List of hypothetical technologies
- List of paradoxes
- List of philosophical problems
- List of undecidable problems
- List of unsolved deaths
- List of unsolved problems in astronomy
- List of unsolved problems in biology
- List of unsolved problems in chemistry
- List of unsolved problems in computer science
- List of unsolved problems in economics
- List of unsolved problems in fair division
- List of unsolved problems in geoscience
- List of unsolved problems in information theory
- List of unsolved problems in mathematics
- List of unsolved problems in medicine
- List of unsolved problems in neuroscience
- List of unsolved problems in physics
- List of unsolved problems in statistics
- Lists of problems
- Unknowability