The use of high energy megavoltage photon beams alone or in combination with low energy mega voltage X-ray beams and/or electron beams has become a standard practice in the radiation treatment of cancer for selected disease sites. This multi-modality treatment approach has prompted medical accelerator manufacturers to begin producing treatment machines capable of generating both a low energy megavoltage X-ray beam (e.g. 6 MV) and a high energy X-ray beam (18 MV), in addition to a range of electron beam energies. This paper will review the current methods used in accelerators to produce dual energy X-ray beams and multiple energy electron beam modalities. This overview will also review several of the physical characteristics of these dual energy units.