Virtually all situations require a judgment or decision on the basis of several separate pieces of information. Grading a term paper, evaluating a job applicant, selecting a leader, or simply listening to a speaker, all involve integration of several pieces of information. What rule governs the integration process in human judgment? The present paper presents an overview of the author's experimental work in the area of interpersonal attraction, group perception, leadership, job attraction and satisfaction, attribution theory, and developmental psychology. Findings from these studies clearly suggest that the weighted average principle may be considered as a general pr9ncple of human judgment and decision.