ICSEY is a large international study of the acculturation and adaptation of immigrant youth (aged 13 to 18 years) who are settled in 13 societies (N = 5,366), as well as a sample of national youth (N = 2,631). The study was guided by three core questions: How do immigrant youth deal with the process of acculturation? How well do they adapt? Are there important relationships between how they acculturate and how well they adapt? There were substantial relationships between how youth acculturate and how well they adapt.