1 Université du Québec à Montréal, Québec, Canada.
2 HSE University, Moscow, Russia.
3 Concordia University, Montreal, Québec, Canada.
4 Jewish General Hospital, Montreal, Québec, Canada.

A focal point in the acculturation literature is the so-called "integration hypothesis," whereby integration (high mainstream cultural engagement and heritage cultural maintenance) is associated with higher psychosocial adjustment, compared to other strategies. Yet, the vast majority of this literature is cross-sectional, raising questions about how best to understand associations between integration and adjustment. Does greater integration lead to greater psychosocial adjustment, as proposed by the integration hypothesis? Or is it the other way around, with more adjustment leading to greater integration, consistent with what we name the "mental resources hypothesis?" This study tests these 2 competing hypotheses in a 4-wave longitudinal study of 278 international students in their first weeks and months in Canada. The results replicate well-documented cross-sectional acculturation-adjustment associations. They also show that baseline adjustment is prospectively associated with later integration and mainstream acculturation, but not vice versa, supporting the mental resources hypothesis but not the integration hypothesis.