In this systematic review, we review the evidence for the effects of altitude training on endurance performance, the physiological mechanisms behind its effects, successful and unsuccessful methods of altitude training, and important factors associated with its effectiveness. The purpose of altitude training is to build fitness based on the premise that altitude training will increase aerobic capacity through adaptation, such as increased red blood cell production and improved mitochondrial efficiency. The review summarizes disparate findings from different sports and training regimens, yet, provides both positive and liability of the benefits of such approaches. Altitude training outcomes are influenced critically by the factors of altitude level, training duration, intensity and individual acclimatization. A promising approach discussed is 'live high train low' where athletes have the advantage of hypoxia benefits while continuing high intensity training at lower altitudes. Even with all that evidence of altitude training, the review recommends more work be done to find optimal protocols and produce more consistent, long-term results about how altitude training affects endurance performance. Additionally, a number of studies point to a positive benefit of training at high altitude but living at low altitude (called 'live high, train low') in which athletes can optimize their altitude adaptive advantages while continuing intense training at sea level. Finally, the review calls for more research on optimal protocols of altitude training and its long-term effect on endurance performance, since the evidence is contradictory on different sports and training regimens.