Cognitive diversity and the related notion of shared cognition are two of the most influential concepts in research on group processes and performance. In this article, we develop a more nuanced view of cognitive diversity/sharedness that distinguishes between cognitions held at implicit and explicit levels. The central argument is that because individuals posses independent implicit and explicit beliefs relating to a task, group members can hold similar explicit mental models while simultaneously possessing dissimilar implicit representations. Drawing on a contemporary dual system view of cognition, we theorize the consequences for group process and performance when: (i) members hold similar explicit mental models but dissimilar implicit beliefs (illusory concordance), and (ii) when members hold similar implicit beliefs but divergent explicit mental models (surface discordance). The analysis yields various propositions concerning the effects of illusory concordance and surface discordance on group decision making (i.e. alternative generation, group consensus, and commitment to choices) and group coordination (i.e. cohesion and interdependence in task performance). We discuss the implications of our analysis for measuring shared cognition in organizations and developing cognitive heterogeneity/ homogeneity in work groups and teams and outline potential directions for future research on the interaction among implicit and explicit cognition.