Groups are formed when two or more individuals interact and work together to achieve common objectives. There are various theories around how and why groups form. Groups can be formal or informal, and go through typical stages of development including forming, storming, norming, performing, and adjourning. A group's structure, which includes its leadership, roles, norms, size, status, and composition, shapes member behavior and group performance. Group processes like communication, decision-making, and conflict also impact a group's functioning.