Focused ion beam machining (FIBM), also termed focused ion beam milling, provides a tool for processing materials on the nanometer scale. It enables selective removal of minute quantities of matter with high spatial resolution in a precisely controlled manner which was hitherto impossible.

Focused ion beam machining instruments have been developed in university and industrial research laboratories over the last 25 years and have been commercially available since the mid-1980s. Functionally, the instruments are similar to a conventional scanning electron microscope (SEM), but use an intense source of ions in place of an electron emitter. Imaging, as in a scanning electron microscope, is done by sweeping the beam pixel-by-pixel across the surface of a specimen in a raster pattern. However, in focused ion beam machining both secondary electrons and secondary ions can be collected to form an image. This provides additional image contrast information when the instrument is operating as a scanning ion microscope (SIM). Deposition of conducting or insulating material on selected areas with nanometer resolution can also be done in the same instrument. Combining focused ion beam maching with focused ion beam deposition (FIBD) provides a means for ultraprecision fabrication, modification, and patterning of materials. Instruments have also been developed which provide dual electron and ion capabilities, using an electron beam for imaging and a focused ion beam for machining and deposition.