The current paper will present an extensive investigation of polymer gear (acetal and nylon) friction and wear behaviour. First, a unique test method for polymer gear wear will be described in brief and later used in the extensive investigation of acetal and nylon gear wear. Initial tests were performed using acetal pinions with acetal gears, and nylon pinions with nylon gears, with further investigation carried out using dissimilar polymer gears. In this case the driver and driven effects on the gear wear behaviour was also considered when dissimilar materials were used. For acetal against acetal gears, it was found that the acetal gear wear rate increased dramatically when the load reached a critical value for a specific geometry and the gear surface showed slow wear, with a low specific wear rate if the gear was loaded below this critical value. It was found that the surface temperature was the dominant factor influencing the wear rate and an initial relationship between gear surface temperature and gear load capacity has been established and further developed. Experimental investigation on nylon gears was also carried out and different failures have been found compared to acetal gears, such as gear root and pitch fractures. The most interesting observation from the experimental work is the significant difference in wear behaviour when running acteal against nylon gears, especially the low wear rate when acetal is used as the driver gear.