Milling is a process of machining with rotary cutters to remove material by moving the cutter into the workpiece. It can be performed in different directions in one or more axes, with different milling head speed and pressure. Milling involves a wide variety of operations and machines, ranging from small individual components to large, heavy milling operations using pick combinations. This is one of the most frequently used processes for machining non-standard workpieces with precise tolerances.

Milling is a cutting operation that uses the cutter to remove material from the workpiece surface. A milling cutter is a rotary cutting tool, often with multiple cutting points. Unlike drilling, where the tool is moved along the axis of rotation, the cutter is usually moved perpendicularly to its axis during milling, so that the cut is made on the perimeter of the cutter. When the cutter enters the workpiece, the cutting edges (grooves or teeth) of the tool repeatedly cut and exit the material, removing chips from the workpiece with each pass. The cutting action consists of a shearing deformation; the material is pushed from the workpiece into tiny lumps which hang together to a greater or lesser extent (depending on the material) to form chips. This makes the metal cutting slightly different (in its mechanics) from cutting soft materials with a blade.

The milling process involves removing the material by making many separate, fine cuts. This is achieved by using a multi-tooth cutter, spinning the cutter at high speed or moving the material through the cutter slowly; most often it is a combination of these three approaches. The speeds and feed rates used vary according to the combination of variables.