This document defines and classifies groups and discusses factors that influence group behavior. It begins by defining a group as two or more individuals interacting and interdependent who have come together to achieve objectives. It then classifies groups into formal, informal, command, task, interest, and friendship groups. Next, it discusses reasons people join groups such as security, status, and goal achievement. The document goes on to describe models of group development including forming, storming, norming, performing, and adjourning stages. It also discusses group structure, focusing on roles, norms, status, size, composition, and cohesiveness. The document concludes by covering group tasks such as decision-making and techniques including interacting groups, brainstorm