This chapter explores the dynamics of groups and teams in organizational settings, highlighting the distinctions between the two and the factors that influence their effectiveness. It introduces three core dimensions affecting group performance: purpose and type, context and composition, and internal processes. The chapter details various group types such as management, project, production, service, and virtual teams and examines how composition, coaching, diversity, and individual knowledge, skills, and abilities shape outcomes. It emphasizes the role of group norms and outlines models of group development, including Tuckman’s five-stage model and the punctuated equilibrium model. Decision-making methods such as brainstorming, the nominal group technique, and the Delphi method are discussed alongside barriers like groupthink, peer pressure, and social loafing. The chapter also addresses contemporary challenges including psychological safety, global collaboration, and cross-cultural teams. Together, these concepts underscore that group and team effectiveness can be learned.