Influence: The Psychology of Persuasion by Robert Cialdini is a classic book that explores the principles of influence and persuasion. Cialdini breaks down the psychology behind why people say 'yes' and provides practical strategies for effectively persuading others. Whether you're in sales, marketing, or any other business role that involves influencing others, this book offers valuable insights into human behavior and how to ethically apply persuasion techniques. With real-world examples and scientific research, Influence is a must-read for anyone looking to improve their persuasive skills.