Molecular Beam Epitaxy (MBE) is widely used by both researchers and industry to produce films of metals, insulators and semiconductors. The principle of MBE is to grow single crystals by using chemical reactions to produce thin layers of materials whose lattice structures are identical to the substrate on which they are deposited. Single or clusters of atoms are heated up in ultra high vacuum (UVH) and deposited onto a hot substrate surface. The process is that the atoms diffuse across the substrate lattice and eventually grow into a very pure film. Thin films of alternating atomic layers can be grown and this technique is limited by its low growth rate compared to other epitaxy methods. This technique is used to fabricate thin films, normally in a research setting, as the process is relatively slow for industry. MBE is an ultra-high vacuum process used to produce high purity thin films with mono layer control. Few examples include quantum wells, spintronics (also called magnetoelectronics), semiconductors, insulators, superconductors and optoelectronics, etc.