Why did the market choose gold as an international standard for money? In his classic book The Theory of Money and Credit, Ludwig von Mises developed a beautiful and comprehensive philosophy of what money is and how it comes about, starting from barter and working all the way through the international gold standard. One of the valuable insights from the book is Mises’s concept of what characteristics are vital to the money function. He focused on five aspects in particular, and understanding them is still valuable today, even in a world of pure fiat money.