"As a Man Thinketh" by James Allen is a self-help book that explores the power of thoughts and their impact on our lives. The book emphasizes the idea that our thoughts shape our character, actions, and ultimately our destiny. Allen argues that by controlling and directing our thoughts, we can achieve success, happiness, and fulfillment in all aspects of life. The book offers practical advice on how to cultivate positive thinking, overcome negative thoughts, and harness the power of the mind to create the life we desire.