This Handbook explores the cognitive, motivational, interpersonal, clinical, and applied aspects of personal uncertainty. It showcases both the diversity and the unity that defines contemporary perspectives on uncertainty in self within social and personality psychology. The contributions to the volume are all written by distinguished scholars in personality, social psychology, and clinical psychology united by their common focus on the causes and consequences of self-uncertainty. Chapters explore the similarities and differences between personal uncertainty and other psychological experiences in terms of their nature and relationship with human thought, emotion, motivation, and behavior. Specific challenges posed by personal uncertainty and the coping strategies people develop in their daily life are identified. There is an assessment of the potential negative and positive repercussions of coping with the specific experience of self-uncertainty, including academic, health, and relationship outcomes. Throughout, strategies specifically designed to assist others in confronting the unique challenges posed by self-uncertainty in ways that emphasize healthy psychological functioning and growth are promoted. In addition, the contributions to the Handbook touch on the psychological, social, and cultural context of the new millennium, including concepts such as Friedman's "flat world," confidence, the absence of doubt in world leaders, the threat of terrorism since 9/11, the arts, doubt and religious belief, and views of doubt as the universal condition of humankind. The Handbook is an invaluable resource for researchers, practitioners, and senior undergraduate and graduate students in social and personality psychology, clinical and counseling psychology, educational psychology, and developmental psychology.