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 techniques for effectively persuading others. Whether you're in sales, marketing, or any other business role that involves influencing others, this book offers valuable insights on how to ethically persuade and influence people. By understanding the principles of influence, you can improve your negotiation skills, sales techniques, and overall communication abilities.