A spirit level or bubble level is an instrument designed to indicate whether a surface is level or plumb. Different types of spirit levels are used by carpenters,stone masons,bricklayer, other building trades workers, surveyors,millwrights and other metalworkers.

Original spirit levels had two banana-shaped curved glass vials at each viewing point and were much more complicated to use. In the 1920s, Henry Ziemann, the founder of Empire Level, invented the modern level with a single vial. These vials, common on most ordinary levels today, feature a slightly curved glass tube which is incompletely filled with a liquid, usually a yellow-colored 'spirit' (a synonym for ethanol), leaving a bubble in the tube. Ethanol is used because of its low freezing point, −114°C, which prevents it from freezing in cold weather. Most commonly, spirit levels are employed to indicate how horizonal (level) or how vertical (plumb) a surface is.

Some are also capable of indicating the level of a surface between horizontal and vertical to the nearest dgree. The crudest form of the spirit level is the bull's eye levell: a circular flat-bottomed device with the liquid under a slightly convex glass face which indicates the center clearly. It serves to level a surface in two perpendicular directions, while the tubular level only does so in the direction of the tube. The most sophisticated spirit levels are guaranteed accurate to five-ten-thousandth of an inch (.0005) per inch and are much easier to read because of their blue colour.

There are different types of spirit levels for different uses:

• Surveyor's leveling instrument
• Carpenter's level (either wood, aluminum or composite materials)
• Mason's level
• Torpedo level
• Post level
• Line level
• Engineer's precision level
• Electronic level
• Clinometer or Inclinometer
• Slip or Skid  Indicator