An instrument is a concrete or abstract tool intended for a purpose other than mechanical work, in particular a refined one.

• Musical instruments are devices designed to produce music, frequently by plucking or striking a string or bell or drum surface, or by forcing air to resonate (see wind instrument).
• Scientific instruments are devices intended to assist in the conduct of science. An example would be the test tubes and other glassware one might find in a chemistry or biology laboratory.
• Measuring instruments are devices used to measure or compare the magnitude of physical properties, such as voltmeters.
• Analytical instruments are devices used to measure multiple or complex material properties, such as mass spectrometers.
• Medical instruments are devices for the diagnosis and treatment of diseases, such as stethoscopes.
• Legal instruments are documents used to formally document various types of transactions or confirm certain statuses for specific purposes, such as confirming contractual relations, civil status, etc. Examples include wills, writs, court order, contracts, treaties, marriage licenses and driver's licenses.
• Financial instruments are documents used to formally document various types of financial transactions. Examples include loan agreements, bonds, mortgages, stocks and floating charges.