Studies have now conclusively linked impaired sperm function with reactive oxygen species attack on sperm-a process more commonly referred to as "oxidative stress". While research studies suggest that up to 80% of infertile men have evidence of oxidative stress, the majority of fertility specialists do not test their patients for oxidative stress, nor offer empirical antioxidant treatment. This is primarily due to a lack of availability of oxidative stress testing in the majority of clinical andrology laboratories, and a general ignorance of the importance of oxidative stress as a cause of male infertility amongst treating physicians. The first aim of this chapter is to outline the causes of oxidative stress so that they may be identified by simple history and examination. Sentinel signs of oxidative stress seen on routine semen analysis are then reviewed, together with a discussion of the benefits and pitfalls of direct testing for sperm oxidative stress. Finally, the management of sperm oxidative stress is outlined, including improvements in lifestyle, better management of underlying chronic illness, antioxidant medical therapy and surgical approaches to oxidative stress.