"The Wealth of Nations" is a seminal work by Adam Smith, first published in 1776. In this book, Smith explains how individuals acting in their own rational self-interest in a free-market economy can lead to economic prosperity for society as a whole. This idea is famously captured in the concept of the invisible hand, where the pursuit of individual gain results in the overall economic well-being of society.
Therefore, "The Wealth of Nations" is the correct answer.