Dementia has enormous impacts on the quality of life of people with this condition and their carers. As the population ages, the numbers affected will increase considerably. A major challenge is how to provide high-quality treatment and support to these individuals in ways that are valuable to them, and at a cost considered by society to be affordable. We examined in a recent study for the G7 Legacy Event, held in London in June 2014, the economic consequences of different ways to respond to the challenge posed by the rising numbers of people with dementia. We prepared a fully costed description of the care and support for people with dementia in the UK today. We compared this with four alternative scenarios: two of these scenarios represent arrangements that are worse than today, and two of them better. We used simulation modelling to compare these scenarios: our model calculates the overall cost and quality of life consequences over one year for the UK; and our illustrative lifetime model calculates the cost and quality of life impacts from the point when people develop dementia until they die. Data to populate the models were extracted from various UK and other sources, including epidemiological studies, descriptions of care and support patterns, randomised trials of specific interventions and expert opinion. Included in these sources are individual-level data from a dozen recent UK dementia trials and observational studies. Our new analyses suggest that the annual cost of dementia in the UK in 2015 will be approximately £21 billion (at 2012/3 price levels). More than a third of this total is the (imputed) cost of unpaid care provided by family and other carers. Dementia also has major impacts on quality of life of both the estimated 800,000 people with dementia in the UK in 2015 and their carers. 48 We have recently started a new study in which we plan to to generate new evidence to inform policy and practice so as to better meet needs, promote the wellbeing of people with dementia and their carers, and achieve efficiency in the use of resources. We will develop a comprehensive set of models to estimate current and future needs, outcomes and costs, drawing on methods from a range of disciplines, with the involvement of people with dementia and their carers. An important outcome will be a publicly available legacy model for others to use. Individuals and stakeholders will be able to make their own projections of needs for care and support.