When retrieving a quote from memory, evaluating a testimony’s truthfulness, or deciding which products to buy, people experience immediate feelings of ease or difficulty, of fluency or disfluency. Such “experiences of thinking” occur with every cognitive process, including perceiving, processing, storing, and retrieving information, and they have been the defining element of a vibrant field of scientific inquiry during the last four decades. This book brings together the latest research on how such experiences of thinking influence cognition and behavior.