A molecular beam refers to any type of ray or stream of molecules moving in the same direction, typically in a vacuum inside an evacuated chamber. It is created when a gas at a higher pressure is allowed to expand through a small orifice into a low-pressure chamber. This leads to the formation of a beam of particles, moving with equal velocities and few collisions. The molecules of a molecular beam are manipulated by the use of magnetic and electrical fields. These beams can be used to create thin films in molecular beam epitaxy. They are also used to fabricate structures such as quantum dots, quantum wells and quantum wires. This book elucidates the concepts and innovative models around prospective developments related to molecular beams. From theories to research to practical applications, studies related to all contemporary topics of relevance to these beams have been included herein. Those in search of information to further their knowledge will be greatly assisted by it.