This work adopts a perspective that construes acculturation as a dynamic intergroup process, and social contact with members of the new community as a key mechanism underlying cultural adaptation. We argue that migrants’ initial self-reported mainstream cultural orientation constitutes an important antecedent of early social participation in the new community. Results from two longitudinal studies of newly arrived international students (N = 98 and N = 60) show that more positive initial mainstream cultural orientations prospectively predict higher social participation, specifically in the mainstream group, over the following months. This relation held after controlling for important alternative predictors, namely, extraversion/shyness, mainstream language proficiency, and respiratory sinus arrhythmia, a physiological index of social engagement capacity. These studies focus on the very initial stages of the temporal dynamics of acculturation, contribute to bridging research on acculturation and on intergroup relations, and establish a link between cultural orientations, a subjective attitudinal construct, and concrete social engagement behaviors.