The second edition of this handbook explores the social, 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. Featuring chapters written by distinguished scholars from a range of disciplines in psychology, this book explores 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. It takes an interactionist perspective to examine what social and personality psychology knows about the experience of self-uncertainty in its various forms, exploring its determinants and consequences within and across individuals and groups. The new edition has been extensively revised and updated and includes new material on self-uncertainty within intimate relationships, in groups, and within spiritual and educational contexts. There is also new content on conspiratorial thinking as well as on the uncertain self within the broader context of uncertainty associated with the COVID-19 pandemic. 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. Featuring cutting-edge theory and research on the determinants, experiences, and consequences of uncertainty in the self, 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.