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 follow-up weekly surveys, then 9 monthly follow-up surveys, as well as to an optional cognitive task. The cohort includes more than 1,300 adolescents aged between 13 and 18, as well as over 500 parents, totalling more than 1,800 participants, who resided in many different countries around the world at baseline. Within the sample, 80.0% reported living in the United Kingdom, 13.7% did not provide country of residence, and of the remaining participants, 13 countries were represented by a single participant. Among the participants reporting United Kingdom as country of residence, the average age of adolescents was 15.55 years and 76.9% were female, and the average age of parents was 46.59 years and 86.0% were female.