The ARC study collected data from adolescents and parents of adolescents from March 2020 to August 2021 on mental health, resilience and wellbeing, COVID-19-related experiences, and pandemic anxiety. Following a baseline survey, participants were invited to 11 weekly follow-up surveys, then 9 monthly follow-up surveys, and an optional cognitive task. The cohort includes more than 1,300 adolescents aged 13-18, as well as over 500 parents, for a total of more than 1,800 participants who resided in many countries around the world at baseline. Within the sample, 80.0% reported living in the United Kingdom, 13.7% did not provide their country of residence, and the remaining participants were from 13 countries, each represented by a single participant. Among the participants reporting the United Kingdom as their country of residence, the average age of adolescents was 15.55 years, and 76.9% were female; the average age of parents was 46.59 years, and 86.0% were female.