Brain ageing is a strong risk factor for many neurodegenerative and psychiatric illnesses, with age serving as the greatest risk factor for illnesses such as Alzheimer’s disease and Parkinson’s disease. This chapter reviews the evidence that cortico-basal ganglia and cortico-cerebellar circuitry deteriorates with age, and highlights similarities between neurodegenerative illnesses and ageing that support the contention that cortico-basal ganglia and cortico-cerebellar networks decline in ageing. Ageing is also associated with ataxia. Cerebellar ataxia accounts for 8% of gait disorders in ageing, most commonly due to cerebrovascular disease. While most research into cortico-basal ganglia and cortico-cerebellar connectivity is focused on dysconnectivity in neurodegenerative diseases, substantial evidence suggests both networks deteriorate in healthy ageing. Cortico-basal ganglia, cortico-cerebellar circuits and the interaction between them support important motor and non-motor cognitive processes. These circuits deteriorate with age, resulting in subtle but similar impairments to those found in neurodegenerative illnesses.