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 ...

With coins, supplies are limited either because they are very old, were minted in very limited supplies, or contain errors or ...

The L.E. Bruun Collection has been insured for 500 million Danish kroner, or around $72.5 million.

You don’t usually see errors with proof coins, but there are exceptions. One involved 1975 dime proof sets, which that lacked an “S” mintmark (from the San Francisco Mint).