This is a list of puzzles that cannot be solved. An impossible puzzle is a puzzle that cannot be resolved, either due to lack of sufficient information, or any number of logical impossibilities.
15 Puzzle – Slide fifteen numbered tiles into numerical order. Impossible for half of the starting positions.
Five room puzzle – Cross each wall of a diagram exactly once with a continuous line.
MU puzzle – Transform the string MI to MU according to a set of rules.
Three cups problem – Turn three cups right-side up after starting with one wrong and turning two at a time.
Three utilities problem – Connect three cottages to gas, water, and electricity without crossing lines.
Thirty-six officers problem – Arrange six regiments consisting of six officers each of different ranks in a 6 × 6 square so that no rank or regiment is repeated in any row or column.