The novel Coronavirus (COVID-19) pandemic has placed an overwhelming burden on health systems and public health authorities to respond with effective interventions, policies, and messages. In the absence of a vaccine or treatment, behavioural mitigation strategies (e.g., social distancing, handwashing, face masks) perceived to be critical to slowing the spread of COVID-19 have been implemented. Little is known about the impact of the COVID-19 pandemic on the behaviour, mental health, and wellbeing, particularly in vulnerable populations (BAME, older adults), and those with underlying medical conditions, or those living in socioeconomically deprived regions. Families are experiencing substantial changes in their daily routine and social infrastructure. The World Health Organization (WHO) have published general recommendations for parents about mental health and wellbeing during the COVID-19 outbreak. However, poll/questionnaire studies do not typically target parental attitudes or behaviours. Therefore, a significant unanswered question is **“What are the mental health and well-being consequences of the COVID-19 lockdown for vulnerable and medically-complex populations?”** The objective of this proposal and the **A**ttitudes **A**bout **C**OVID-19 and **H**ealth (**ATTACH**) study is to assess changes in cognition (i.e. thoughts and beliefs), behaviour (e.g. compliance with measures, barriers to seeking and receiving effective treatment), psychological well-being (e.g., anxiety, social isolation) and health-related quality of life (HRQOL) in both general and vulnerable populations. We will collect data via an established smartphone survey app (AMO; “Air My Opinion”) and use embedded REDCap (Research Electronic Data Capture) links to online questionnaires. Our design will allow us to determine differences between groups, assess change over time, as well as to capture and model the long-term impact of COVID-19 and mitigation strategies on behaviour, mental health, and HRQOL. We will also use publicly available postal district geodata to examine interactions with local social and economic factors. Our recruitment strategies will aim to oversample participants in BAME communities and those with medical conditions. Poll results and health-related resources will be displayed on the AMO and ATTACH websites. These data will have a significant impact by enabling unprecedented real-time insights into individual psychological and behavioural responses that can be translated into targeted interventions to decrease the current spread of COVID-19 and increase overall wellbeing, and will also provide knowledge for future epidemics and pandemics. The ATTACH study team is an international collaboration of clinical psychologists and neuroscientists in the United Kingdom, the United States, and Mexico. We aim to examine results within and across countries to further elucidate how the COVID-19 pandemic is affecting lives. Video: https://youtu.be/A3aJC60ZZBE Twitter: @attachstudy Facebook: @ATTACHCOVID19study Participate: https://bit.ly/attachstudy