Cognitive Stimulation Therapy (CST) for dementia: International implementation in Brazil, India and Tanzania (CST-International) Dementia presents huge financial costs and significantly reduces quality of life for people and their families. However, it remains largely unrecognised and untreated in low and middle income countries. There is an urgent need to introduce simple interventions which can address this treatment gap, something that has been done successfully in other places including the UK. Cognitive Stimulation Therapy (CST) is an evidence-based, group non-pharmacological intervention shown to significantly improve cognitive functioning and quality of life. It can be delivered to a wider population than can medication, as it has no known side-effects, can be delivered by non-medical personnel, does not require specialist equipment or training and is low cost.  This key aim of this project is to create an ongoing and sustainable programme to implement CST in various regions within these three countries. A secondary objective is to increase awareness and skills in the detection and management of dementia, both for health workers and families. We have selected an upper middle income (Brazil), lower middle income (India) and low income (Tanzania) country, to provide a broad range of economic as well as geographical and cultural challenges. All three countries have already a) previously translated and adapted the CST manual, following the same (recommended) process, b) begun or completed initial testing, with positive results and c) engaged local stakeholders and gathered initial ideas on implementation. In each country, (i) we will investigate the things that are likely to help or hinder implementation of CST. We will interview a range of people including clinicians, policy makers and people with dementia and their families, enabling a rich perspective. (ii) We will develop an implementation strategy for each region included, but with shared themes across all sites. (iii) We will test this strategy through looking at how well it works. We will train CST trainers and attempt to recruit 50 people with dementia in each country (150 in total) into CST groups. We will see whether people attend the sessions, enjoy the sessions and whether facilitators are able to run sessions as intended. We will measure outcomes including cognition and quality of life in people with dementia and look at the costs of running groups in each setting. A three hour family educational session, developed as part of this study; will be offered by the researchers to all families of those who were screened and not included in the study, and to those who participate (after completion of follow-up measures, hence avoiding impact on outcomes). Wherever possible, this will be offered in a group format, both to encourage communication between family members and for the economy of time. People may be offered further support such as physical examinations, depending on the setting, needs and availability of resources (iv) Our testing phase will enable us to adapt and improve our implementation strategy, which we will then disseminate both locally, nationally and internationally. This will include published training manuals, a sustainable CST training programme, ongoing CST groups with ongoing sources of referral, financial arrangements and, if applicable, changes in policy. We hope that, more broadly, the work will result in increased knowledge and awareness of screening, diagnosing and treating dementia, with recommendations of routine outcome measures. This will be achieved through the CST training, the screening procedures, the CST intervention and the family education session. The Global Challenges Research Fund (GCRF) supports cutting-edge research to address challenges faced by developing countries. The fund addresses the UN sustainable development goals. It aims to maximise the impact of research and innovation to improve lives and opportunity in the developing world.