This chapter discusses the cognitive spectrum associated with ageing, ranging from successful ageing to severe cognitive impairment impacting on activities of daily living such as seen in dementia. Dementia prevalence increases with age and carries the same risk factors as those for cardiovascular disease, such as midlife high cholesterol, body mass index and blood pressure, as well as inactivity and smoking. The chapter reviews studies investigating physical activity and exercise interventions that may improve cognition in older people. It describes the different forms of cognitive ageing, ranging from normal ageing to dementia, and review attempts to treat impaired cognitive function using activity. The chapter provides an updated review on the association between physical activity (PA) and cognitive decline or dementia, in prospective, longitudinal studies of older adults (= 55 years of age).