Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other gases. Cutting fluids are made from petroleum distillates, animal fats, plant oils, water and air, or other raw ingredients. Depending on context and on which type of cutting fluid is being considered, it may be referred to as cutting fluid, cutting oil, cutting compound, coolant, or lubricant.

Most metalworking and machining processes can benefit from the use of cutting fluid, depending on workpiece material. Common exceptions to this are cast iron and brass, which may be machined dry (though this is not true of all brasses, and any machining of brass will likely benefit from the presence of a cutting fluid).

The properties that are sought after in a good cutting fluid are the ability to:

• Keep the workpiece at a stable temperature (critical when working to close tolerances). Very warm is acceptable, but extremely hot or alternating hot-and-cold are avoided.
• Maximize the life of the cutting tip by lubricating the working edge and reducing tip welding.
• Ensure safety for the people handling it (toxicity, bacteria, fungi) and for the environment upon disposal.
• Prevent rust on machine parts and cutters.