The book is an anthropological history of money. I wouldn't say it has a single thesis, although the idea that money has arose out of debt-relationships in different periods is a recurring theme. It starts in Babylon, where he looks at how temples acted as debt-registrars for cities and how this evolved into a currency system. He moves forward through history and theorizes why some periods are dominated by intrinsically valuable currency (boullion) vs. paper notes or other more abstract stores-of-value. I believe the final chapter covers the 1970s after Nixon moved off the gold standard.