The primary objective of this review is to provide an overview of how overtraining and the overtraining syndrome (OTS) affect the immune system of athletes. A secondary objective is to provide sports medicine clinicians with guidance as to how best to prevent and/or treat some of the health consequences of overtraining and the OTS as related to the development of a compromised immune system associated with exercise training. The OTS is a physically debilitating condition that results in athletes being totally compromised in their capacity to perform and compete. Many physiological systems are affected by the process of overtraining and the OTS; but one system in particular, the immune, is highly susceptible to degradation resulting in a reduction in overall health and performance. Monitoring of an athlete's exercise training load and other life stresses is critical to the determination of when their training regimen may be excessive, thereby increasing the risk of OTS developing. Taking steps to mitigate prolonged exposure to extreme stress (training + life or otherwise) in athletes as well as promoting a healthy immune system can significantly aid in the advancement of an athlete's training regimen progression and ultimate physical performance and overall health. In this light, this review provides approaches to aid sports medicine clinicians in promoting a healthy immune system in athletes.