The aim of this project is to unravel the evolution and functionality of the avian cerebellum by integrating avian brain genetics with comparative phylogenetic methods. A major feature of the hindbrain of all vertebrates is the cerebellum. This brain region plays an important role in motor control, but its involvement in cognitive functions and emotional responses is becoming more recognised and has increased interest in this area of the brain in recent years. The size of the cerebellum (both absolute and proportional to the rest of the brain) varies greatly both between and within species and has been linked with its functionality. To date, the mechanisms underlying the control of cerebellum size and to what degree size is linked to functionality is unknown. Using the large expansion of the cerebellum (both absolute and proportional) that occurred during domestication in chickens, this project will identify causative genes for cerebellum size. This will be done using a combination of expression QTL analyses, whole-genome resequencing and functional studies of candidate genes on an intercross population between domestic chickens and their wild progeny. Additionally, this project will assess the role of the cerebellum between species and how its size has changed throughout evolution using phylogenetic comparative methods. The findings I will obtain from this project will elucidate the mechanisms that control proportional cerebellum size in birds and the functional role of cerebellum size, knowledge which can be extended onto other animal classes.