We don’t always know how to help people, even when those people are our friends. This is not just a problem about how to provide the help we know others need. It is also the problem of what help they need in the first place, and this is a problem that requires ethical thinking. The theory of well-being defended in this book—the value fulfillment theory—provides a solution to this problem. In short, the theory says that our lives go well to the extent that we succeed in terms of what matters to us emotionally, reflectively, and over the long term. In other words, well-being consists in fulfilling or realizing our appropriate values over time. Therefore, according to the value fulfillment theory, when we want to help others achieve greater well-being, we should pay attention to their values. This means attending to how others’ values fit together, how they understand what it means to succeed in terms of these values, and how things could change for them over time. Being a good and helpful friend, then, requires cultivating some habits of humility that overcome our tendency to think we know what’s good for other people without really understanding what it’s like to be them. This work presents the first book-length defense of value fulfillment theory. It is aimed at philosophers and psychologists, and anyone with an interest in philosophical research on human well-being.