Groups serve important functions for organizations and individuals. There are formal and informal groups, as well as groups defined by tasks, commands, interests and friendships. People join groups for security, status, self-esteem, affiliation, power and goal achievement. Groups develop through forming, storming, norming, performing, and adjourning stages. Roles, norms, status, size, composition and cohesiveness determine a group's structure. Effective group decision making requires consideration of techniques like brainstorming, nominal groups and electronic meetings to avoid issues like groupthink.