Molecular beam epitaxy (MBE) is a process to fabricate crystalline heterostructures for the study of novel physical properties and solid-state device technology. In an MBE machine, a chamber is evacuated of all gases to a final pressure in the ultra-high vacuum (UHV) range (<10^-11 Torr). Such low pressures are necessary to ensure that contaminants do not end up in our samples. The heterostructures are then grown with atomic-layer precision.  By minimizing contamination and controlling growth at the nanometer level, the MBE machine is able to produce high-quality samples that allow physicists to explore novel phenomena.