Formal work groups: groups that organizations establish to facilitate the achievement of organizational goals. Informal groups: groups that emerge naturally in response to the common interests of organizational members: stages of group development, forming, storming (conflict often emerges, norming (members resolve issues that provoked the storming, performing (task accomplishment, adjourning. Punctuated equilibrium model: a model of group development that describes how groups are affected by their first meetings and crucial midpoint transitions. Upper limit of # of group members = 300-400, most groups have between 3-20. People are usually more satisfied in small groups vs. large groups. Additive tasks: tasks in which group performance is dependent on the sum of the performance of individual group members. Disjunctive tasks: tasks in which group performance is dependent on the performance on the best group member. Process losses: group performance difficulties stemming from the problems of motivating and coordinating larger groups. Actual performance = potential performance process losses.