A Ponzi scheme is a type of investment fraud. It works by paying returns to earlier investors with money from newer investors. Instead of generating legitimate profits from a business venture, the scheme operator just shuffles money around. The whole operation relies on a constant stream of new cash to survive.

This type of fraud is named after Charles Ponzi, who became notorious for a scheme he ran in the early 1920s. He promised investors an incredible 50% return in just 45 days. His plan involved buying international postal reply coupons in other countries and redeeming them for a higher value in the United States. While the underlying business idea was plausible, it was not profitable at the scale he claimed.

Instead of actually running the business, Ponzi simply used the money from new investors to pay off the earlier ones. The news of high returns spread like wildfire, and money poured in. For a short time, the illusion of success was maintained, but the math was always destined to fail.

The basic structure of a Ponzi scheme is simple but deceptive. It starts with a central operator who pitches a secret, complex, or exclusive investment opportunity that promises unusually high returns.

Early investors put money in and receive the promised returns on schedule. These returns aren't profit, though—they're just a portion of the money from newer investors. Satisfied and impressed, the early investors often reinvest their money and tell friends and family about the amazing opportunity.

This word-of-mouth advertising is crucial. It brings in a wave of new investors, providing the cash needed to continue paying the earlier ones. The operator can keep the scheme going as long as more money is coming in than is being paid out. But this is an unsustainable model. It requires an exponential increase in new investors to keep up with the promised payments. Eventually, the scheme runs out of new money and collapses, leaving the majority of investors with nothing.