Bitcoin - The First Solution to Establishing Trust Over an Untrusted Network

Until now, middlemen were necessary to fight what is called the double spending problem. What I'm moving from me to you is just an entry on a secure public ledger. Public ledger is maintained by a set of computers all talking to each other using a protocol. So I don't have to worry about some bank giving me an IOU and then taking that IOU and handing it to another bank.