In his first book, "The Theory of Moral Sentiments", Smith proposed the idea of an invisible hand - the tendency of free markets to regulate themselves through competition, supply and demand, and self-interest.
He is known for creating the gross domestic product (GDP) concept and his theory of compensating wage differentials.
In 1776, Smith published "An inquiry into the nature and causes of the wealth of nations" shortened to "The wealth of nations."
In "The Wealth of Nations", Smith popularised many ideas that form the basis for classical economics.