The extent to which technology may be able to support people with dementia and their carers along the care pathway and in different care settings is of interest to policy makers and governments. In this paper we provide an overview of the role of technology in dementia care, treatment and support by mapping existing technologies - by function, target user and disease progression. Technologies identified are classified into seven functions: memory support, treatment, safety and security, training, care delivery, social interaction and other. Different groups of potential users are distinguished: people with mild cognitive impairment and early stages of dementia, people with moderate to severe dementia and unpaid carers and health- and social care professionals. We also identified the care settings, in which the technologies are used (or for which the technologies are developed): at home in the community and in institutional care settings. The evidence has been drawn from a rapid review of the literature, expert interviews and web and social media searches. The largest number of technologies identified aim to enhance the safety and security of people with dementia living in the community. These devices are often passive monitors, such as smoke detectors. Other safety interventions, such as panic buttons, require active intervention. The second largest number of interventions aims to enhance people's memory and includes global positioning systems devices and voice prompts. These technologies mostly target people in the early stages of dementia. A third group focusing on treatment and care delivery emerged from the literature. These interventions focus on technology-aided reminiscence or therapeutic aspects of care for people with dementia and their carers. While the review found a range of technologies available for people with dementia and carers there is very little evidence of widespread practical application. Instead, it appears that stakeholders frequently rely on everyday technologies re-purposed to meet their needs.