Think and Grow Rich by Napoleon Hill is a self-help book first published in 1937. Arguably one of the most famous and well-known books on self-improvement, the book has sold over 15 million copies. Inspired by wealthy businessman Andrew Carnegie, Think and Grow Rich was published during the Great Depression and contains the philosophy of rich people and how they made their wealth. 

Hill in this book had devised sixteen 'laws' that need to be applied to achieve success. The book takes those laws, and puts them into fourteen principles that the reader can develop. Along with basic advice such as treating your customers well, etc, Hill also tells us that we need to grow spiritually. The book, after all, is called Think and Grow Rich.