You may have seen one of the many headlines about valuable pennies in circulation. "Lincoln Wheat Penny Worth $124M You Could ...

A gigantic gold coin made for Spain’s King Philip III in 1609 has become Europe’s most valuable coin after selling for more than £2.6 million at an auction in Switzerland.

As with just about any asset, a coin’s value is determined by its market demand. This means that coins in short supply often see higher demand — and higher values. With coins, supplies are limited ...