Cylinder may refer to:

• Cylinder (geometry), a three-dimensional geometric shape
• Cylinder (algebra), the cartesian product of a set with its superset
• Cylinder (engine), the space within which a piston travels in an engine
• Cylinder (steam locomotive)
• Cylinder, a unit of data division on a hard disk drive:
  • Another term for tracks in the Cylinder-head-sector hard disk addressing method
  • A Cylinder (disk drive) of an IBM CKD disk
• Hydraulic cylinder, a cylinder barrel with piston rod for pushing and pulling using pressurized fluid
• Pneumatic cylinder, a cylinder barrel with piston rod for pushing and pulling using compressed gases
• Gas cylinder, containers used to store compressed gases or compressed air
• Diving cylinder, a type of gas cylinder used in Scuba diving
• Graduated cylinder, glassware used for measurement of liquids in laboratories
• Phonograph cylinder, the dominant medium of audio storage from the 1870s to the 1910s and in limited use (such as in the dictaphone) through the mid 20th century
• Cylinder (firearms), the rotating device that contains the firing chambers of a revolver
• Cylinder lock, the part of a lock that is profiled to accept a specific key
• A type of lens and a form of refraction error
• Cylinder, Iowa, a small city in the United States