Group Dynamics refers to the study of human behavior in groups. There are primary and secondary groups, command and task groups, and in-groups and out-groups. Groups can be deliberately created to perform tasks, with hierarchies and rules guiding behavior. Informal groups form the company grapevine to ease stress. Group dynamics involve stages of forming, storming, norming, performing, and adjourning. Effective group decision making uses techniques like brainstorming, nominal groups, Delphi, and dialectic methods. Roles in groups include task roles like information giving and seeking, and relationship roles like encouraging participation and relieving tension.